Water Injection Optimisation for Matured Waterflood Reservoir: A Case Study for Value Creation from Improved Production Performance and Cost Savings

摘要

This paper will highlight the study, implementation and results of water injection optimization program in a matured waterflood reservoir prior to the implementation EOR IWAG tertiary recovery. The scope included analytical understanding of current reservoir condition, reservoir simulation study for various injection proposals, historical injection facilities performance and the optimization/remediation proposal to increase WIM (Water Injection Module) uptime, and reservoir surveillance requirement to ensure the water injection optimization program meet its objectives. Low current offtake rate in the reservoir, low WIM uptime, high cum. VRR and an imbalance in the reservoir pressure between the Eastern and Western flanks of the reservoir necessitated a study on the WIM program/schedule to optimize the injection by redistributing the injection volume between the Eastern and Western injectors and identify opportunities for cost saving through WIM shut-off. A history matched model was used to evaluate different injection scenarios. Collaboration between Subsurface and Surface Facilities Team enabled a coherent plan for periodical WIM shut-off and maintenance activities to be designed in order to deliver higher WIM uptime. The proposals for the injection optimization program were: 1. Apply '1 Month Off - 2 Months On' Injection Cycle, starting April 2017. 2. Increase avg. water injection target to 15 -20 kbwpd as per full WIM capacity. 3. Re-balance the injection volume between Eastern and Western injectors by ratio of 3:1. 4. Maintain WIM/Injection uptime consistently above 76% during injection months. The results from the optimization exercise (May 2017 - December 2017) were encouraging and better than expected from simulation run. Production decline from producing well was successfully arrested with cum. oil gain from the period totaling approximately 18 kbbls (50 bopd annualized). The reservoir pressure in the Eastern flank was increased to reach the level similar with the Western flank. The value creation from additional production gain and cost savings of WIM shut-off was around USD 1.4 MM. It can be safely concluded that the injection optimization plan has successfully achieved its objectives. The novel idea and approach from this exercise was the demonstration of how a simple understanding of a reservoir and its associated surface injection performance can provide an opportunity for a quick and simple optimization plan to be implemented to improve the sweep efficiency of the injection by targeting the unswept/bypassed oil and subsequently increase the oil production from producing well(s).