Water alternative gas(WAG) optimization for a heterogeneous Brazilian pre-salt carbonate reservoir
气水交替（WAG）是一种循环过程，涉及交替注入水和气体，其主要目标是通过保持初始高压力，减缓水和气体的突破速度，降低油相粘度，从而提高油藏的采收率。本研究旨在在一个含有轻质油的碳酸盐油田上应用和优化WAG策略，将其与最初计划的注水策略进行比较，并调查WAG改善油田产量的能力。
在该研究中，使用了GEM组分油藏模拟器来模拟通过向油藏注入气体进行WAG过程，并采用与优化的注水策略相同的井身结构。随后，创建了一个WAG策略，优化了井的数量和位置，以便比较这两种开采方法。WAG优化涉及对底孔压力（BHP）、WAG循环持续时间、最大气油比（GOR）和井位置等变量进行详细评估，以实现高净现值（NPV）。
该研究侧重于在非常规储层，特别是盐下碳酸盐储层中应用WAG优化模拟，并调查其对生产策略和预测的影响，强调其在最大化NPV和油田恢复量方面的潜力。结果显示，与注水相比，WAG改善了油藏开发效果。这个解决方案显示出在不确定性（如储层非均质性、断层、裂缝、缝洞等）下进行测试的潜力作为未来的发展方向。
关键词：气水交替、非均质性、盐下碳酸盐储层、WAG优化。
巴西坎皮纳斯大学机械工程学院石油研究中心
Abstract
Water alternating gas (WAG) is a cyclical process that involves alternating water and gas injections with the primary goal to improve sweep efficiency by maintaining initial high pressure, slowing water and gas breakthrough, and lowering oil viscosity. The objective of this work is to apply and optimize a WAG strategy on a carbonate field with light oil, compare it to the initially planned water-flooding strategy, and investigate the capability of WAG to improve field production. In this research, a compositional reservoir simulator was used to model a WAG process by injecting produced gas into the reservoir, using the same well structure as an optimized water-flooding strategy. Subsequently, a WAG strategy was created, optimizing the number and locations of wells, to facilitate a comparative analysis of the two recovery methods. The WAG optimization involved a detailed assessment of variables such as bottom hole pressure (BHP), WAG cycle duration, maximum gas oil ratio (GOR), and well positioning, to achieve a high net present value (NPV).
The study focuses on the application of WAG optimization modeling in unconventional reservoirs, specifically pre-salt carbonate reservoirs, and investigates its implications on production strategy and forecast, emphasizing its potential for maximizing NPV and oil recovery in a recently producing field. The results showed that WAG improved reservoir performance when compared to water injection and produced a greater amount of oil. This solution showed potential to be tested under uncertainties (reservoir heterogeneity, faults, fractures, karsts, vugs, etc.) as future steps. Keywords: water alternating gas; heterogeneous; pre-salt carbonate reservoir; WAG optimization.
