Development of A Multi-Completion-Gas and Downhole Water Sink-Assisted Gravity Drainage MC-GDWS-AGD Process to Enhance Oil Recovery and Reduce Water Cresting in Reservoirs With Strong Water Aquifers
Authors: Al-Tammimi Mohammad A. , Al-Maliki Sadeq Y. , Alabody Mustafa J. , Al-Mudhafar Watheq J. , Wood David A. , Wojtanowicz Andrew K. 
Published: April 2022

The Gas and Downhole Water Sink-Assisted Gravity Drainage (GDWS-AGD) process functions to enhance oil recovery by placing vertical gas injectors at the top of the reservoir combined with a series of horizontal wells located in the lower part of the reservoir for oil and water production. The injected gas accumulates to form or enhance a gas cap, while oil and water drain by gravity towards the base of the reservoir due to their heavier densities. To further enhance oil recovery, and to overcome the economic limitations of using vertical gas injectors, multi-completion production wells can also be used for gas injection through their annulus sections. This novel configuration thereby achieves Multi Completion-Gas and Downhole Water Sink-Assisted Gravity Drainage (MC-GDWS-AGD). The feasibility of MC-GDWS-AGD is investigated in this study by numerical simulation of the heterogeneous PUNQ-S3 reservoir, which is surrounded and supported by strong aquifers.

The MC-GDWS-AGD process aims to minimize water cut in oil production wells from offshore reservoirs with bottom water drives and strong water coning tendencies. In the combined technologies, the gas is injected through the annulus of 7-inch production casings at the top of the reservoir. Then the same casing is dually completed for two 2-3/8 inch horizontal tubing strings: one above the oil-water contact for oil production, and one beneath that contact to function as the water sink. The two completions are hydraulically isolated within the wellbore by a packer. The lower (water sink) completion employs a submersible pump and water-drainage perforations. The submersible pump drains the accumulation of water from around the well. By doing so it prevents the water from breaking through into the oil column and adversely affecting production through the horizontal oil-producing perforations. The heterogeneous multilayered PUNQ-S3 reservoir, which is surrounded by infinite aquifers, was considered to simulate this process. The MC-GDWS-AGD process simulation is designed to evaluate oil flow rate, cumulative oil production, and water cut in oil production wells. The simulation compares the performance of MC-GDWS-AGD with the GAGD and GDWS-AGD completion configurations.

The simulation results reveal similar performance for the MC-GDWS-AGD and GDWS-AGD configurations, for all the parameters considered. The GDWS-AGD method slightly outperforms the MC-GDWS-AGD method by achieving a small increase in cumulative oil production from 1.8x 106 m3 for the GAGD method to 1.83x 106 m3. Both methods exceeded primary recovery in terms of cumulative oil production. Water cut decreased from 74% in the GAGD method to 63% in the MC-GDWS-AGD process. The oil recovery factor achieved by the MC-GDWS-AGD process increased by about 8% compared to that achieved by the GAGD method. The value of the MC-GDWS-AGD process is associated with its effectiveness to improve oil recovery by reducing the water coning, water cut, and improving gas injectivity, and at the same time reducing well costs. This new process allows for gas injection, oil, and water production to be conducted through a single multi-completed wellbore. This configuration also leads to multiple additional economic benefits, some of which are associated with the reduction of operational surface facilities in offshore oil fields.