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Home My WebLink About2020 Prudhoe Oil and Put River Oil PoolsI ANNUAL RESERVOIR SURVEILLANCE REPORT WATER AND MISCIBLE GAS FLOODS PRUDHOE OIL POOL AND PUT RIVER OIL POOL & ANNUAL RESERVOIR PROPERTIES REPORT PRUDHOE AND PUT RIVER OIL POOLS JANUARY THROUGH DECEMBER 2020 2020 ANNUAL RESERVOIR SURVEILLANCE REPORT PRUDHOE BAY AND PUT RIVER OIL POOLS CONTENTS SECTION 1.0 INTRODUCTION 2.0 OVERVIEW 3.0 PRESSURE UPDATE 3.1 Pressure Monitoring 3.2 Pressure Plan 4.0 PROJECT SUMMARIES 4.1 Prudhoe Waterflood/PBMGP 4.2 Gas Cap Water Injection Project 4.2.1 Observation Well Cased Hole Saturation Logs and Zonal Conformance 4.2.2 2020 Surveillance Plans 4.2.3 Plans for Change in Project Operation 4.3 Put River Pool 5.0 GAS MOVEMENT SURVEILLANCE 5.1 Gas Movement Summary 6.0 REVIEW OF POOL PRODUCTION ALLOCATION FACTORS 2020 ANNUAL RESERVOIR SURVEILLANCE REPORT PRUDHOE BAY AND PUT RIVER OIL POOLS LIST OF EXHIBITS 1-A Prudhoe Bay Unit Field Schematic 1-B PBU Well Statistics 1-C PBU Production / Injection Statistics 1-D PBU Pressure Map 1-E Areally Weighted Average Pressure Plot 1-F Areally Weighted Pressure Data 1-G Average Monthly CGF MI Rates and Compositions 2 Fieldwide Reservoir Balance 3 Wells Surveyed for Gas Movement 4 Pressure Surveys (Form 10-412) 5-A GCWI Surveillance and Extent 2020 5-B GCWI 2020 Extent: Southwest – Northeast Section 5-C GCWI 2020 Extent: North – South Cross Section 6 Annual Reservoir Properties Report-Prudhoe and Put River Oil Pools (AK 20 AAC 25.270) 7 Put River Sandstone Distribution 2020 ANNUAL RESERVOIR SURVEILLANCE REPORT PRUDHOE BAY AND PUT RIVER OIL POOLS 1.0 INTRODUCTION As required by Conservation Order (CO) 341I and CO 559A, this report provides a consolidated waterflood and gas oil contact report summary of the surveillance activities for the Prudhoe Oil Pool waterflood project, Miscible Gas and Gas Cap injection projects, and the Gravity Drainage Area within the Prudhoe Oil Pool, plus a section for the Put River Pool. The time period covered is January through December of 2020. In keeping with the requirements of the Conservation Orders, the report format provides information for the Prudhoe Bay waterflood /PBMGP EOR project and the gravity drainage project in the field, where applicable. As approved by the AOGCC on March 15, 2021, separate sections for production and injection summaries are not provided for each of the five flood areas within the Prudhoe Oil Pool. However, Exhibits 1-D, 1-E, and 1-F contain pressure analysis for each of the flood areas to provide assurance of sufficient voidage replacement. Information included is as follows: •Analysis of reservoir pressure surveys and trends •Progress of the enhanced recovery projects, including the gas cap water injection project •Voidage balance by month of produced and injected fluids •Data on Minimum Miscibility Pressure (MMP) of injected miscible gas •Summary of Returned Miscible Injectant (RMI) volumes •Results of gas movement and gas-oil contact surveillance efforts •Results of pressure monitoring efforts The Annual Reservoir Properties Report-Prudhoe and Put River Oil Pools is being submitted under cover of this report as Exhibit 6. (AK 20 AAC 25.270). The Excel version is also being submitted electronically to aogcc.reporting@alaska.gov. A report of completed development or service wells that have been shut-in for 365 days or longer as of January 1, 2020, will be separately filed with the Commission by March 31, 2020, in accordance with 20 AAC 25.115. Production and injection data is provided for the PBMGP project area along with information on the GCWI in the Gravity Drainage region and the Put River Oil Pool. A separate section has been provided with detailed information on gas-oil contact surveillance. As agreed in 2004 with the Commission, the discussion of Gas Production Mechanisms was not included in the report. 2020 ANNUAL RESERVOIR SURVEILLANCE REPORT PRUDHOE BAY AND PUT RIVER OIL POOLS 2.0 OVERVIEW Exhibit 1A identifies the five flood areas and gravity drainage areas in the Prudhoe Oil Pool as follows: FS-2, EPWZ, WPWZ, NWFB, EWE, and GD. The Waterflood Project encompasses all five flood areas. The Prudhoe Bay Miscible Gas Project (PBMGP) is currently active throughout the waterflood areas. The Eileen West End waterflood pilot concluded in March 1999, after successfully establishing EWE injection potential. EWE information since waterflood startup in September 2001 is included in this report. As previously mentioned, production and injection data is not subdivided into the five flood areas for this report. Exhibits 1-B and 1-C provide well, production, and injection statistics for the Prudhoe waterflood area. The well counts reflect the total number of wells that contributed to production or injection during the report period. During the report period of January through December 2020, field production averaged 166.6 MBOD, 7452.9 MMSCFD (GOR 44742 SCF/STB), and 1149.2 MBWD (water-cut 87.34%). Overall injection during this period averaged 1818 MBWD with 147.4 MMSCFD of miscible gas injection. Exhibit 1-D provides analysis of pressure static, buildup, and falloff data that was collected from 2018 through 2020 at a datum of 8,800 ft, subsea for the Ivishak Formation. Using the three-year rolling technique improves the statistical validity of the pressure distribution since it roughly triples the number of data points employed versus only using the current year static pressures. As in the past, abnormal pressures, such as pressures taken in fault compartments and in the Sag River Formation have been removed. AOGCC Conservation Order No. 341I, Rule 12 (c) specifies that “The minimum miscibility pressure (MMP) of the Miscible Injectant must be maintained at least 100 psi below the average reservoir pressure in the Prudhoe Bay Miscible Project area. When the Operator demonstrates that the reservoir pressure is no longer declining within the Prudhoe Bay Miscible Project Area (as evidenced by reservoir pressure measurements), the MMP may be maintained at or below the average reservoir pressure in the Prudhoe Bay Miscible Project area.” As MMP became the constraint on NGL production in the winter of 2018, and the reservoir pressure has stabilized with the gas cap water injection project, the MMP limit was increased from 3150 psi to 3200 psi in March of 2019. We are investigating the overall benefit of further diluting PBMI, but the current setpoint is still set below the average reservoir pressure in the Prudhoe Bay Miscible Project area. There are two MI analyzers at Prudhoe Bay CGF (4901 and 4951). Historically, MI data from MI analyzer 4901, which was installed at the discharge of the MI compressors, were reported in the past ASR's. However, from June to September 2020, analyzer 4901 was out of calibration and the ethane measured by this analyzer was too high. Hence the data from this analyzer were not used in 2020 ASR. Instead, the data reported in exhibit 1-G were derived from analyzer 4951 which was installed at the suction of the MI compressors. The only difference is that analyzer 4051 does not see the lean gas blend which happens at the compressor discharge. Therefore, 2020 ANNUAL RESERVOIR SURVEILLANCE REPORT PRUDHOE BAY AND PUT RIVER OIL POOLS corrections have been made to include the effect of blendback on MI composition and MMP using the blend back ratio and lean gas composition. Analyzer 4901 was repaired in October 2020 and has been functioning normally since then. The raw compositional data used to calculate MMP are reviewed and engineering judgement is applied to remove poor data associated with 0 or very low MI volumes and brief upset periods to provide the monthly average MMP provided in Exhibit 1-G. Exhibit 2 provides monthly and annual fieldwide reservoir balance figures. On March 5, 2020 the Commission approved the Seawater Optimization Project (SWOP) which was implemented in the 2020 plan year in DS-1 and DS-12 of the Eastern Peripheral Wedge Zone (EPWZ). The Commission specified the following two conditions: Condition 1 states that BPXA is required to include in the Annual Reservoir Surveillance report for the POP and PROP: “a detailed description of the progress towards returning the PROP to production“. As the SWOP project was implemented during the plan year of this report (January – December 2020), a description of this plan is included in section 4.3 of this report. Condition 2 states that the ASR is to also include “the evaluation of the potential to improve ultimate recovery by ceasing water injection elsewhere in the POP”. Continued evaluation of a more extensive shut-in of injection within the Prudhoe Bay Miscible Gas Project (PBMGP) area took place in 2020 and will continue into 2021. Water injection at DS-01 and DS-12 that was shut-in with the implementation of SWOP was sourced with seawater which was redirected to GCWI with existing infrastructure. Water injection elsewhere in POP is nearly all produced water and alternative injection locations must be identified to maintain water handling capacity and avoid oil production impacts. Reservoir simulation studies are ongoing to evaluate alternate injection locations and potential for improved oil recovery. 2020 ANNUAL RESERVOIR SURVEILLANCE REPORT PRUDHOE BAY AND PUT RIVER OIL POOLS 3.0 PRESSURE UPDATE 3.1 Pressure Monitoring Exhibit 4 (Form 10-412) provides pressure, buildup, and falloff data collected in 2020 at a datum of 8,800 ft, subsea used for the Ivishak Formation. During 2020, per CO 341I, as modified by the Commission on July 20, 2016, use of calculated BHP’s from surface data in injectors are permitted. All of these new data are listed in Exhibit 4 as “FL”. Inclusion of the reasonable surface calculated data, based on consistency of the results, confirms an elevated pressure area in the Gas Cap associated with the GCWI project.For this report, as in the past, pressures taken in fault compartments, the Sag River Formation, and in Zone 1 of the G-Pad LPA (Low Pressure Area), which don’t appear to be in good communication with the rest of the reservoir, have been excluded from Exhibit 1-D. Also excluded were wells shut-in less than a week that had not stabilized as compared to offsetting statics. Other wells completed in Zone 1 and Zone 4B, which are in poor communication with the rest of the reservoir and therefore have lower pressures, were still included in the map and calculations if their shut-in times were deemed long enough. The excluded pressure measurements are listed separately in Exhibit 4. Unless otherwise noted, all pressure calculations are areally weighted, bound by the main field original 50' LOC contour, and are referenced to a pressure datum of 8,800' SS. It was agreed with the commission that the polygon pressures would be calculated differently starting with the 2005 report, than it had in past reports due to the advent of pressure response to gas-cap water injection. That methodology consisted of utilizing only the pressure gathered during the reporting period. Starting with the 2009 report, since the field pressure has stabilized, pressure points from a rolling three-year period were used to construct the pressure map so as to reduce the statistical variation induced by changing year-to-year well sets. Exhibit 1-D illustrates the 2020 pressure map using 2018 through 2020 data points. As shown in Exhibit 1E, the historic pressure decline appears to have stabilized due to gas-cap water injection. For 2020, average pressure in the PBMGP project areas using three years of pressure static measurements was calculated to be 3404 psia by areal weighting, as compared to 3369 psia in 2019. The GD area pressure was stable decreasing 5 psi from 3319 psia in 2019 to 3314 psia in 2020 (Exhibit 1F). This subtle pressure decrease is within the expected statistical variation with a different annual pressure sampling data sets. 3.2 Pressure Plan Per CO 341I Rule 6a, the following pressure surveillance plan information is provided. Prudhoe Bay reservoir depletion strategies are defined, and the goal of the pressure program is to optimize areal coverage and provide sufficient data for well safety and reservoir management. The plan for 2021 calls for collection of a minimum of 20 pressure surveys fieldwide. In accordance with the rule (5% clause), a minimum of 1 pressure surveys will be collected in each of the seven development areas: Gas Cap, Gravity Drainage, Flow Station 2 Water/MI Flood (MWAG) Project, Eastern Peripheral Wedge Zone MWAG Project, Western Peripheral Wedge Zone MWAG Project, Eileen West End Waterflood Project, and the Northwest Fault Block MWAG Project. 2020 ANNUAL RESERVOIR SURVEILLANCE REPORT PRUDHOE BAY AND PUT RIVER OIL POOLS Given Commission approval for Seawater Optimization Project (SWOP) and project execution in 2020, focus will be placed on obtaining pressure measurements in the vicinity of DS-1 and 12 areas in order to monitor changes resulting from waterflood cessation at Flow Station 1. 4.0 PROJECT SUMMARIES 4.1 Prudhoe Waterflood / PBMGP During the report period of January through December 2020, production from the waterflood area averaged 78.3 MBOD, 1580.5 MMSCFD and 987.5 MBWD (water-cut 92.7%). Overall Waterflood injection during this period averaged 902.8 MBWD with 145.9 MMSCFD of miscible gas injection. The waterflood area’s GOR increased from an average of 19,716 SCF/STB in 2019 to an average of 20,185 SCF/STB in 2020. The water cut increased from an average of 92.1% SCF/STB in 2019 to an average of 92.7% in 2020 Cumulative water injection in the five major projects from waterflood startup through December 2020 was 13916 MMSTB, while cumulative MI injection was 3422 BCF. Cumulative production in these same areas (not including Gravity Drainage) since waterflood startup was 3107 MMSTB oil, 15911 BCF gas, and 10335 MMSTB water. As of December 31, 2020, cumulative production exceeded injection by -11042 MMRB compared to -10006 MMRB at the end of 2019. Under- injection is related to production of free gas influxing from the gravity drainage region which should not be replaced so as to maintain a steady declining gas contact. Similar to last year, production and injection values have been calculated based upon the waterflood start-up dates for the project areas rather than for each injection pattern. A breakdown of the production and injection data with cumulative figures is provided in Exhibit 1-C for the report period. Interpreted MI breakthrough has occurred in 87 wells during the reporting period. The previous year showed interpreted MI breakthrough in 59 wells. RMI production is an indicator of EOR pattern performance and the presence of RMI is best determined by primarily gas sample analyses that show a separator gas composition richer in intermediate range hydrocarbon components but also proximity to WAG injectors in known MI patterns. MI breakthrough in a WAG pattern well is considered to have occurred when the average RMI rate over the number of producing days in a well exceeds 200 MCF/D. 2020 ANNUAL RESERVOIR SURVEILLANCE REPORT PRUDHOE BAY AND PUT RIVER OIL POOLS 4.2 Gas Cap Water Injection Project Details of the volume of water injected into the Gas Cap during 2020 are shown below; units in thousands of barrels of seawater injected per month (MBWPM): PSI-01 PSI-05 PSI-06 PSI-07 PSI-08 PSI-09 PSI-10 Total 1/1/2020 3,296 3,104 3,784 1,008 2,989 2,991 2,898 20,070 2/1/2020 3,259 2,968 3,635 967 2,826 2,917 2,741 19,313 3/1/2020 3,249 3,033 3,665 1,020 2,992 3,029 2,579 19,567 4/1/2020 3,296 3,054 3,746 981 3,054 3,177 2,730 20,038 5/1/2020 3,464 3,144 3,829 1,006 3,121 3,218 2,942 20,725 6/1/2020 3,324 3,055 3,743 815 3,066 3,139 2,934 20,077 7/1/2020 3,479 3,157 3,654 869 2,983 3,025 2,893 20,061 8/1/2020 2,578 2,346 2,855 641 2,305 2,355 2,220 15,300 9/1/2020 1,966 1,785 2,206 1,779 1,794 1,845 1,802 13,177 10/1/2020 2,512 2,247 2,778 2,553 2,275 2,389 2,273 17,027 11/1/2020 3,352 3,077 3,803 3,559 3,126 3,235 3,145 23,297 12/1/2020 3,202 2,960 3,734 3,474 3,013 3,129 3,011 22,524 The 2020 volume of sea water injected in the PSI wells was 231.2 million barrels. The cumulative volume injected at the end of 2020 was 3.0 billion barrels of sea water since the project startup in 2002. 4.2.1 Observation Cased Hole Saturation Logs and Zonal Conformance Pulsed neutron logs (RPM, RMT, etc) run in offset producers continue to be the primary method of monitoring water movement from the Gas Cap Water Injection project. Many of these wells have had several repeat logs since injection began. By comparing the latest neutron logs with the baseline and previous logs, the presence of injected water can be readily observed. This procedure has provided a very clear picture of water in the Ivishak Formation and allows the monitoring of vertical and lateral movement of the waterfront. Exhibit 5-A is the locator map for the GCWI area and shows the PSI injectors along with the observation wells. The turquoise polygon indicates the interpreted current GCWI waterfront, which has very minimal change since 2018. Well 02-38A, south of the mid-field graben, started producing water in late 2017, and chemistry analysis suggests it is likely GCWI. It was this datapoint in 2017 that resulted in the slight extension of the polygon across the mid field graben. A log was run in this well in 2019, with data collected down through Z1A, and there was no evidence of water. It is likely that the perforations near the toe, which are closer to the mid field graben, are the source of the GCW production. The information from all the neutron logs was used to develop the updated northwest-southeast 2020 ANNUAL RESERVOIR SURVEILLANCE REPORT PRUDHOE BAY AND PUT RIVER OIL POOLS and north-south cross sections (Exhibits 5-B and 5-C) showing the interpretation of the surveillance data for the current time period. The most recent round of neutron log surveillance included the following wells: 05-01C, 18-01A, L2-16, and L2-25. As the areal and vertical extent of the water mass becomes larger, the rate of incremental advancement both laterally and vertically has become noticeably slower. At this point, the changes in the waterfront have followed a relatively predictable pattern established in recent surveillance, where the largest extent of incremental waterfront coverage appeared in Zone 2C, owing to significant lateral continuity of the 24N shale. Surveillance wells for 2020 saturation monitoring were chosen for sufficient coverage to monitor GCW extent, as well as better refine understanding of the water movement into the producing zones 1A and 1B. Many wells in the DS18 area are producing GCW. Understanding the water pathway to Zone 1, which is the oil bearing interval in this far upstructure area of the field, is a continued focus for future logging and analysis. Integrating production evidence with log evidence is an important part of the analysis. Future surveillance will continue to include repeat neutron logs for monitoring the maximum lateral extent of the flood front, monitoring water movement within each zone, and specifically in the producing Zone 1. No DS18 wells started producing GCW for the first time in 2020. 4.2.2 2021 Surveillance Plans GCWI Injectors Injection pressures, rates, and temperatures are recorded for each well every day. Pressure-rate plots will be routinely monitored for changes in injectivity of the wells. Observation Well Cased hole Saturation Logs This program will continue as it has in the past by running cased hole saturation logs every year with the final timing and locations determined based on the results to date. Gravity Survey A gravity survey is not planned for 2021. 4.2.3 Plans for Change in Project Operation As a result of SWOP implementation and increased operational efficiency at the Seawater Treatment and Injection Plants (STP/SIP), sea water rates greater than the initial project scope of 650 mbwpd (annual average) can be injected. The full field model indicates additional recovery associated with higher injection volumes in the gas cap based on a fieldwide pressure increase. The desired annual average GCWI target volume for 2021 is 700 mbwpd, contingent upon AOGCC approval. Further details on long term rate and/or pressure targets will be provided with the sanctioning of PAVE. 2020 ANNUAL RESERVOIR SURVEILLANCE REPORT PRUDHOE BAY AND PUT RIVER OIL POOLS 4.3 Put River Oil Pool On November 22, 2005 the AOGCC ruled in Conservation Order 559 that the Western, Central and Southern Lobes of hydrocarbon bearing Put River sands would be defined as the Put River Pool and that the Northern Lobe would be included in the Prudhoe Oil Pool. Exhibit 7 displays all four lobes which are in pressure isolation from each other. Additional technical information was previously supplied with the application which led to Conservation Order 559. On December 19, 2019, the AOGCC granted BPXA’s request to: (1) to administratively amend Conservation Order 559A to contract the Put River Oil Pool (PROP) to the area encompassed by the Southern Lobe of the Put River sandstone; (2) to modify rule 18 of CO341H to ensure that the downhole commingling ruled authorization that currently allows downhole commingling of any well in the PROP with the Prudhoe Oil Pool will continue to apply to wells completed within the currently established bounds of the PROP when the affected area of the PROP is contracted; and (3) a gas oil ratio exemption to wells completed in the Central and Western lobes of the Put River sandstone for the purposes of collecting data to develop a reservoir development strategy for those sands in accordance with 20 AAC 25.240(b)(3). 2020 Production and Injection For the year 2020, about 61% of the production, and all of the injection, occurred in the Southern lobe, with the remaining production from well 15-41B which has perforations in the Western and Central lobes. Production from the Put River Oil Pool in 2020 averaged 237 BOPD averaged across calendar days. The total 2020 production of the Put River Pool comes from two Put River producers: wells 02-27A and 15-41B. Injection in the Southern Lobe of the Put River averaged 2,252 BWPD for the days the injector was online and 1,403 BWPD averaged across calendar days. Cumulative Put River water injection is 14.1 MMBW, of which 514 MBW was injected in 2020. All Put River Southern Lobe injection has been from well 01-08A. 01-08A was shut-in in August 2020 and remains shut-in due to the execution of the SWOP project. As a result of the injector shut-in, the Put River Southern Lobe producer 02-27A was also shut-in. The 2020 cumulative production for the Put River Oil Pool was 87 MBO, 496 MBW and approximately 1,799 MMSCF formation gas. The full life cumulative production for the Put River Oil Pool through December 31, 2020 was 4.3 MMBO, 9.2 MMBW, and approximately 8.3 BSCF formation gas. (Note that these cumulative volumes include a technical estimate, based on material balance calculations, of Southern lobe production from a casing leak in 02-27 between 1994-1997. The cumulative gas volume reported in this report is reflective of the best technical estimate of the formation gas production from the PROP; the volume reported in previous ASRs may differ due to accounting for the estimated casing leak volumes and gas lift volumes.) Since the commencement of SWOP and the shut-in of all injection at Flow Station 1, options have been evaluated to restore the PROP to production, including drilling, workover, and non-rig wellwork options to allow for resumed injection into the PROP. We are also evaluating the operational feasibility of alternative sources of injection water including pit dewatering to satisfy voidage replacement requirements needed to resume production from the PROP. In the 2020 ANNUAL RESERVOIR SURVEILLANCE REPORT PRUDHOE BAY AND PUT RIVER OIL POOLS meantime, while we evaluate our options, we will continue to monitor the reservoir by obtaining a static bottom hole pressure in one of our three Put River Southern Lobe wells in 2021 to observe the pressure behavior during the shut-in period. For this report (and also for last year’s 2019 ASR), the reservoir properties in Exhibit 6 for the PROP pertain to the Southern lobe only. 2020 Pressures Put River Oil Pool affected area pressures taken during 2020 are listed in Exhibit 4. The PROP Southern Lobe pressure obtained in 02-23A producer in June 28, 2020 measured 3,839 PSI at - 8,100’ SSTVD. The fairly stable pressure was a result of a voidage replacement ratio of approximately 1 on average for the year. 2021 Surveillance Plan PROP affected area (Southern Lobe) – A stable pressure trend was observed in 2020 as a result of injection near VRR of 1. Since August 2020, both the producer 02-27A and the injector 01-08A have been shut in since the execution of the SWOP project. A static bottom hole pressure survey is planned in 2021 for producer 02-23A, producer 02-27A, or injector 01-08A to observe the pressure behavior in the Put River Southern Lobe during this period of no injection or production. 2020 ANNUAL RESERVOIR SURVEILLANCE REPORT PRUDHOE BAY AND PUT RIVER OIL POOLS 5.0 GAS MOVEMENT SURVEILLANCE The report on gas movement surveillance activities and interpretations provides an overall summary of gas influx movement and summarizes the 2020 gas-monitoring logging program. 5.1 Gas Movement Summary Fieldwide GOC surveillance continues with collection of open-hole and cased-hole logs and monitoring of well performance. In order to monitor gas movement in the reservoir, GOC estimates are made across the field and are based upon the ongoing monitoring program and historical well performance. The central portion of the field, the gravity drainage area (GD) exhibits in some areas almost total influx of the LOC (Light Oil Column). In many areas of the GD a distinct GOC no longer exists. Rather the data suggest that there is a continuous gradation of gas saturation throughout this part of the reservoir. Gas influx is essentially absent in the southern peripheral regions as a result of water and WAG injection in the waterflood areas. There are areas downdip of the GDWFI area that are affected by gas. It has become difficult in most parts of the field to define a single current GOC as the surface is commonly broken into a series of oil lenses and gas underruns beneath the shales. The reservoir is better characterized by a description of remaining oil targets. The targets within the GD occur within three general regions; the basal Romeo (Zones 1 & 2A) sands, the inter-underrun sands, and oil lenses within the expanded GOC. Production from the Romeo (Zones 1 & 2A) sands has historically been low compared to the more prolific upper zones. This interval has a lower net to gross, lower permeability and more limited sand connectivity than the rest of the reservoir. These factors impede gas expansion into the Romeo. Underruns beneath shales within the Romeo sands are likely to be local. The inter-underrun sands occur throughout the GD and are characterized by one or more underruns or solution gas pockets segmenting the remaining oil pad. Gas underruns are observed beneath the top of the Sadlerochit reservoir, under Zone 4 shales, and the most regional persistent underruns have developed under the mappable floodplain shales of Tango or Zone 2B. Oil within the expanded GOC occurs in lenses above regionally continuous shales. Such lenses have been identified from neutron logs. Many lenses continue to exhibit oil drainage over time, while others appear isolated. Exhibit 3 lists the open and cased-hole neutron logs, as well as RST logs, run in the Prudhoe Oil Pool (POP) during the gas-influx reporting period from January 2020 through December 2020. A total of 20 gas-monitoring logs were run in the POP of which 18 were cased-hole and 2 were open- hole. On July 20, 2016 the Commission modified the neutron log requirements in CO 341F Rule 7 (341F.002 (Corrected)) to provide that either cased or open hole neutron logs are useable to fulfill the minimum requirements of 40 neutron log surveys to be run annually. On January 9, 2018 the commission further modified the neutron log requirements in CO 341F (.007) Rule 7 to have the Annual Reservoir Surveillance Report contain the number and approximate locations of neutron log surveys anticipated for the next calendar year. The 2019 ASR committed to a minimum of 30 neutron saturation logs to be run in 2020; however, due to the COVID-19 pandemic and market conditions the commitment was modified to 15 logs for 2020. 2020 ANNUAL RESERVOIR SURVEILLANCE REPORT PRUDHOE BAY AND PUT RIVER OIL POOLS For plan year January 1, 2021 until December 31, 2021, a minimum of 15 neutron saturation logs will be obtained with the following approximate distribution: Gas Cap-3, Gravity Drainage-5, Gravity Drainage Waterflood Interaction-5, Downdip Areas Affected by Gas-2. 6.0 Review of Pool Production Allocation Factors Prudhoe Oil Pool (POP) and Put River Oil Pools Monthly Average Oil Allocation Factors: 2020 Oil Allocation Factor Jan 0.96 Feb 0.95 Mar 0.96 Apr 0.95 May 0.95 Jun 0.95 Jul 0.95 Aug 0.93 Sep 0.93 Oct 0.93 Nov 0.92 Dec 0.92 The table contains monthly averages of oil allocation factors from the 7 facilities that receive production from these two pools: GC-1 (POP only), GC-2 (POP only), GC-3 (POP only), FS-1 (POP & PUT), FS-2 (POP only), FS-3 (POP only) LPC (POP only). Any days of allocation factors of zero were excluded. These allocation factors range from 0.92 to 0.96. Daily allocation data and daily test data are being retained. 2020 ANNUAL RESERVOIR SURVEILLANCE REPORT PRUDHOE BAY AND PUT RIVER OIL POOLS 2020 ANNUAL RESERVOIR SURVEILLANCE REPORT PRUDHOE BAY AND PUT RIVER OIL POOLS Exhibit 1-B PBU Well Statistics Exhibit 1-C PBU Production / Injection Statistics 2020 ANNUAL RESERVOIR SURVEILLANCE REPORT PRUDHOE BAY AND PUT RIVER OIL POOLS 2020 ANNUAL RESERVOIR SURVEILLANCE REPORT PRUDHOE BAY AND PUT RIVER OIL POOLS 2020 ANNUAL RESERVOIR SURVEILLANCE REPORT PRUDHOE BAY AND PUT RIVER OIL POOLS 2020 ANNUAL RESERVOIR SURVEILLANCE REPORT PRUDHOE BAY AND PUT RIVER OIL POOLS Exhibit 1-F Areally Weighted Average Pressures DATE FS2 EPWZ WPWZ NWFB GD EWE PBMGP Dec-77 3935 4005 4016 3944 3999 3968 Jul-78 3870 3967 3978 3909 3963 3914 Dec-78 3832 3930 3944 3875 3933 3873 Jul-79 3813 3895 3911 3843 3901 3844 Dec-79 3791 3861 3879 3799 3871 3816 Jul-80 3799 3831 3848 3770 3856 3798 Dec-80 3852 3819 3822 3781 3823 3818 Jul-81 3881 3821 3799 3814 3809 3840 Dec-81 3880 3815 3799 3820 3793 3842 Jul-82 3872 3806 3800 3812 3778 3833 Dec-82 3850 3795 3797 3804 3762 3818 Jul-83 3831 3784 3792 3787 3745 3804 Jan-84 3814 3771 3783 3772 3728 3790 Jul-84 3796 3758 3777 3756 3711 3774 Jan-89 3779 3743 3771 3736 3695 3755 Jul-89 3760 3730 3763 3723 3678 3740 Jan-90 3732 3708 3731 3704 3658 3713 Jul-90 3708 3693 3716 3687 3641 3695 Jan-91 3680 3676 3694 3655 3623 3666 Jul-91 3642 3657 3673 3628 3605 3635 Jan-92 3617 3641 3652 3602 3588 3615 Jul-92 3591 3626 3632 3577 3570 3593 Jan-93 3561 3600 3619 3544 3549 3582 Jul-93 3543 3595 3598 3515 3531 3565 Jan-94 3539 3555 3578 3483 3512 3537 Jul-94 3523 3536 3555 3456 3492 3516 Jan-95 3496 3524 3555 3507 3482 3506 Jul-95 3473 3507 3536 3489 3466 3486 Jan-96 3466 3485 3497 3478 3446 3463 Jul-96 3450 3467 3472 3461 3430 3443 Jan-97 3446 3484 3460 3444 3404 3441 Jul-97 3429 3467 3438 3427 3387 3421 Jan-98 3452 3417 3417 3421 3379 3430 Jul-98 3435 3409 3394 3402 3363 3415 Jan-99 3445 3391 3382 3343 3339 3443 Jul-99 3429 3378 3360 3317 3323 3426 Jan-00 3406 3361 3372 3268 3294 3418 Jul-00 3390 3351 3353 3240 3273 3395 Jan-01 3366 3325 3325 3225 3274 3358 Jul-01 3360 3310 3309 3205 3257 3347 Jan-02 3325 3334 3289 3163 3270 3358 Jul-02 3312 3324 3273 3144 3245 3347 2020 ANNUAL RESERVOIR SURVEILLANCE REPORT PRUDHOE BAY AND PUT RIVER OIL POOLS Jan-03 3299 3316 3262 3121 3236 3696 3297 Jul-03 3285 3306 3245 3118 3223 3659 3283 Jan-04 3271 3296 3228 3116 3211 3645 3272 Jul-04 3277 3324 3281 3296 3239 3614 3290 Jul-05 3338 3344 3282 3289 3250 3542 3314 Jul-06 3304 3296 3276 3296 3233 3536 3293 Jul-07 3357 3339 3275 3248 3243 3618 3310 Jul-08 3317 3299 3298 3269 3244 3626 3299 Jul-09 3348 3310 3308 3271 3248 3663 3315 Jul-10 3367 3329 3317 3329 3259 3666 3339 Jul-11 3368 3345 3308 3322 3265 3640 3338 Jul-12 3375 3338 3350 3302 3283 3632 3348 Jul-13 3391 3335 3313 3329 3276 3663 3348 Jul-14 3402 3324 3314 3322 3270 3652 3348 Jul-15 3398 3330 3313 3335 3275 3645 3350 Jul-16 3409 3332 3303 3332 3277 3650 3343 Jul-17 3398 3304 3315 3327 3292 3617 3345 Jul-18 3396 3328 3320 3380 3286 3619 3360 Jul-19 3381 3364 3334 3401 3319 3593 3369 Jul-20 3414 3431 3341 3449 3314 3671 3404 2020 ANNUAL RESERVOIR SURVEILLANCE REPORT PRUDHOE BAY AND PUT RIVER OIL POOLS 2020 ANNUAL RESERVOIR SURVEILLANCE REPORT PRUDHOE BAY AND PUT RIVER OIL POOLS FieldwideProducing Fluids (MMRB)JanuaryFebruaryMarchOil7.26.76.9Free Gas215.6203.1202.2Water35.733.635.3TOTAL258.5243.5244.4Injected Fluids (MMRB)Water52.449.852.5Gas211.5199.6197.9TOTAL263.9249.4250.5Net Injection Volumes = Injection -Production (MMRB)TOTAL5.45.96.1Producing Fluids (MMRB)JulyAugustTotalsOil6.66.379.9Free Gas185.2172.72364.7Water38.337.8436.6TOTAL230.1216.72881.1Injected Fluids (MMRB)Water53.949.1633.5Gas181.1169.22317.8TOTAL235.0218.42951.3Net Injection Volumes = Injection -Production (MMRB)TOTAL4.91.770.1Fieldwide - Exhibit 252.4186.4238.8May6.5194.632.6233.8June6.39.3April6.6189.933.0229.651.9199.4251.3October6.8203.338.1248.2247.410.2November6.6201.339.552.4191.6244.059.6196.7256.3275.660.4223.57.3December7.0227.840.852.5179.1231.6183.334.6224.346.5181.6228.1September6.4185.537.2229.1-1.0283.98.28.93.2 2020 ANNUAL RESERVOIR SURVEILLANCE REPORT PRUDHOE BAY AND PUT RIVER OIL POOLS Exhibit 3 2020 Wells Surveyed for Gas Movement 2020 ANNUAL RESERVOIR SURVEILLANCE REPORT PRUDHOE BAY AND PUT RIVER OIL POOLS Exhibit 4 Pressure Surveys (Form 10-412) 2020 ANNUAL RESERVOIR SURVEILLANCE REPORT PRUDHOE BAY AND PUT RIVER OIL POOLS 2020 ANNUAL RESERVOIR SURVEILLANCE REPORT PRUDHOE BAY AND PUT RIVER OIL POOLS Exhibit 5-A GCWI Surveillance and Extent 2020 2020 ANNUAL RESERVOIR SURVEILLANCE REPORT PRUDHOE BAY AND PUT RIVER OIL POOLS Exhibit 5-B GCWI 2020 Extent: Southwest – Northeast Section 2020 ANNUAL RESERVOIR SURVEILLANCE REPORT PRUDHOE BAY AND PUT RIVER OIL POOLS Exhibit 5-C GCWI 2020 Extent: North – South Section 2020 ANNUAL RESERVOIR SURVEILLANCE REPORT PRUDHOE BAY AND PUT RIVER OIL POOLS Exhibit 6 Annual Reservoir Properties Report-Prudhoe and Put River Oil Pools (AK 20 AAC 25.270) 2020 ANNUAL RESERVOIR SURVEILLANCE REPORT PRUDHOE BAY AND PUT RIVER OIL POOLS Exhibit 7 Put River Sandstone Distribution