Optimizing Wasson ROZ CO2 Flood Pattern Configuration for Capital Efficiency: Case Study of 40-Year Field History

Abstract

The use of CO2 injection to produce oil from the residual oil zone (ROZ) of the Wasson field in the Permian Basin has proven to be highly successful when an appropriate development plan is used. The significant volume of oil in place in the ROZ presents a large target for both reserves addition and CO2 sequestration. More than 60% of the ROZ potential lies beneath the already developed San Andres main oil column (MOC) area, which is under CO2 flooding with varying states of maturity, making it challenging to develop such projects efficiently and economically. Over the past 20 years, different pattern configurations (nine-spot, line drive, five-spot) and completion strategies (commingled injector, injection subsurface flow control devices, dual completion injection, dedicated and hybrid line drive) have been used at the Wasson oil development company (ODC) field to develop the ROZ. The results of these various pattern configurations and completion techniques and their pros and cons are discussed in this paper. Commingled production makes it more difficult to quantify incremental ROZ production and increases uncertainty in the performance forecast of future ROZ projects. The dedicated injectors provide better injection control to MOC and ROZ and improve CO2 utilization, especially where the MOC is mature. In this paper, we present one of the key findings from a detailed analysis of field history that caused Oxy to switch from the original dedicated ROZ development to a hybrid line drive pattern configuration. This novel strategy will have higher CO2 retention and more sequestration potential, better areal sweep efficiency for improved oil recovery, and lower capital and operating cost. It also reduces the likelihood of injector interference, provides a stable injection throughput for a long time, and results in a sustained oil and CO2 production plateau, which leads to more efficient utilization of plant capacity. Using ODC as an example, the total capital, F&D costs, and the number of new injection wells will be reduced by 33%, 35%, and 45%, respectively, for changing all the undeveloped patterns from the dedicated to hybrid line drive option. This novel development strategy improves the chance of promoting contingent resources (not currently considered to be commercially recoverable owing to one or more contingencies) to a higher category and offers higher returns with much lower F&D cost and shorter development time.