This paper focuses on a chemical EOR feasibility study for Raudhatain Zubair (RAZU) reservoir in North Kuwait. The study describes a methodical approach to enable pilot location selection, and a fit-for-purpose modeling strategy to guide the Alkaline Surfactant Polymer (ASP) pilot design decisions. The objective of the pilot is to test in the field that ASP chemicals could mobilize remaining oil and drive it to the producers, where it is captured, produced and separated at the surface. A detailed study was conducted that focused first on mapping out the distribution of remaining oil in the Raudhatain Zubair (RAZU) sandstone reservoir, defining the subsurface uncertainties and identifying key decisions that needed to be addressed for the pilot design. Thereafter, a fit-for-purpose probabilistic dynamic model using a range of inputs based on available rock and fluid field data and ASP parameters from an in-house global Chemical EOR database was built. This model was used to predict the range of production outcomes and aid with pilot design decisions. Based on the stated objective of the pilot, an inverted 5-spot pilot pattern was chosen and a representative area was identified that spanned a reasonable average of field properties. An uncertainty analysis on the pilot pattern revealed that the residual oil saturation to both water and chemical and the remaining oil saturation at the commencement of pilot are the largest uncertainties governing the incremental oil recovery from ASP over water flood. Another significant uncertainty was the presence of an aquifer and the influence of active injectors near the pilot area. Depending on the aquifer strength and heterogeneity of the reservoir, fluid drift and can sweep the chemical slug away from the intended target region of the 5 spot pattern. On the design side, the chosen surfactant concentration in ASP slug, which affects the residual oil saturation to chemical, can result in lower than optimal oil recovery if surfactant losses (via adsorption or chemical consumption) are not adequately managed. Other important decisions are injection rate and pattern size since they affect the incremental recovery due to different swept pore volumes in the pilot pattern. Moreover, the model helped in steering important decisions for the pilot – e.g optimum time to switch to ASP injection after water flood. ASP sector models frequently suffer from being overly complex since they are not tailored to address practical questions that drive key pilot decisions in a timely manner. The unique practical modeling approach presented here focuses on identifying critical uncertainties and pilot design parameters while circumventing the need of detailed laboratory data and a full field model history match.
A downhole fluid analysis prototype module (MRPV) has been developed which measures both asphaltene onset pressure (AOP) and bubblepoint pressure (Pb). This manuscript describes one of many recent downhole jobs which were part of a study to characterize live crude oil in real time while sampling mobile oil in a permeable tar mat. These jobs support an enhanced oil recovery (EOR) study to understand the best way to extract bypassed oil (Fatma 2019). In this manuscript, downhole bubblepoint and AOP measurements made with the MRPV in well RA-0Y37 agree with those obtained in a laboratory with bottomhole samples. The effect of oil-based mud contamination on the AOP and Pb is examined during clean up while sampling. Water was present for all jobs, but the hydrophobic membrane blocked water from entering the MRPV, facilitating ease of interpretation of optical data. This manuscript comprises the first part of a two-part series (Tiwari 2020).
Encouraging results from Lab, simulation studies and single well pilot tests (SWCT tests) using ASP flooding provided confidence to conduct multi well pilot test. A confined, normal 5-spot pattern CEOR pilot is planned. SAMA performance over its waterflood life of 17 years has highlighted reservoir heterogeneity in terms of rock and fluids. The paper describes activities performed during pre-pilot phase of drilling 7 pilot wells to de-risk the complexities expected in this carbonate reservoir. Drilling of 7 close spacing vertical well within 5 acre required proper planning and drilling sequence. Out of the seven wells, four corner wells are drilled as injectors and center well as producer. Two observation wells within the pilot area include a sampling well and the other completed with fiberglass casing as a logging well. Data acquisition from coring, formation pressure measurement, sampling, H2S measurement and logging is meticulously planned and quality checked. The main objective of this CEOR pilot is to field test the efficacy of the ASP formulation prepared in the lab. This pilot scale testing would help a better risk assessment and estimate of incremental oil gain due to this technology application. Field-wide implementation of this technology in Sabiriyah Mauddud and other reservoirs in NK will depend on the success of this CEOR Pilot. All 7 EOR pilot wells were successfully drilled despite many challenges using industry’s best practices. Enormous good quality data was generated during drilling of these wells which will aid in understanding the complexity of reservoir within small pilot area and help in implementation of Chemical EOR in Sabiriyah Mauddud reservoir. All the information generated during pre-pilot will be utilized for starting up this CEOR pilot. EOR in carbonate reservoir has been a challenge for the oil industry. These challenges and related risks are mostly attributed to the complexity of reservoir description. Good quality wells and exhaustive information generated during pre-pilot phase did provide valuable insights to de-risk and ensure proper implementation of the Chemical EOR pilot project in a carbonate reservoir which will be a harbinger for North Kuwait’s efforts to exploit EOR reserves.
North Kuwait has vision to increase oil production from its major reservoir and it is planned to be achieved by covering the major reservoirs under the umbrella of enhanced oil recovery (EOR). Sabiriyah Lower Burgan (SALB) is the biggest sandstone reservoir in Sabiriyah field with high permeability and strong aquifer support. Paper describes steps planned from present development strategy of simply infill drilling to EOR to improve the production scenario in future. Primary recovery from reservoirs like SALB are expected to be good. Performance of the reservoir especially rise in water cut of SALB was analyzed which suggested that though primary recovery would be good but will take longer time to achieve. EOR screening was performed and suitable EOR methods were evaluated using mechanistic model. Screening considered target oil, water quality, permeability, oil viscosity, temperature, aquifer and injection capacity. Lab experiments were performed for the identified EOR processes and most suitable method was selected. EOR pilot area and pilot design performed to take it forward from concept stage towards reality. SALB Layered part is an acceptable candidate for EOR process due to favorable mobility ratio which reduces the need for mobility control agents, reservoir being mixed wet system which is encouraging for improving unit displacement efficiency and reservoir rock properties are conducive to most forms of EOR. Low salinity water, CO2, N2 and Chemical EOR methods were evaluated. Mechanistic model based Estimated Recovery factor range for these EOR methods indicated Chemical EOR, (A) SP as most effective EOR method. Lab experiments were performed for CO2, N2 and ASP. In Lab, miscible N2 flooding was not found feasible whereas CO2 flooding was feasible for either as CO2 or a blend of CO2/NGL. Coreflood experiments suggested surfactant-polymer or alkaline-surfactant-polymer pilot flood as promising EOR methods for SALB. KOC has planned to proceed with Chemical EOR with its further evaluation through single well chemical tracer test (SWCTT) as first step. A multi-well pilot was also recommended assuming a successful single wells tracer test which would provide a better understanding of chemical solution injectivity, oil recovery potential, chemical retention by the reservoir, effect of the water drive on alkaline-surfactant-polymer flood potential and operational issues. Target layer and likely area was identified for EOR pilot. EOR in a reservoir with strong aquifer drive has its own challenges but merits of SALB for enhancement of recovery are encouraging. The paper provides an insight of applicability of Chemical EOR in a large reservoir with strong aquifer that will pave the way for similar reservoirs in Kuwait and worldwide.
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