A Methodology for Multilateral-Well Optimization

Abstract

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 183004, “A Methodology for Multilateral-Well Optimization—Field Case Study,” by Ivan Cetkovic, SPE, Majed Shammari, SPE, and Talal Sager, Saudi Aramco, prepared for the 2016 Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, 7–10 November. The paper has not been peer reviewed. Multilateral wells with smart completions controlled by different flow-control technologies offer great operational flexibility, with each lateral able to be operated and optimized independently. Understanding the contribution of each lateral in the complexity of the system was a major objective of this study. In order to optimize the system and predict results under different operational conditions, a multilateral-well-modeling methodology was developed. This methodology covers two main factors affecting multilateral productivity—a flow-dependent gas/oil ratio (GOR) and interference between the laterals. Wells Overview The study was based on multilateral wells complete with inflow control valves (ICVs). As a general description, the wells are completed with three to seven laterals and each lateral is isolated by packers and controlled by an ICV, as shown in Fig. 1. Multilateral-Well Modeling A multiphase surface system flow simulator that is able to optimize production from wells and networks as an integrated system was adapted to generate and optimize the subsurface multilateral-well flow behavior. This simulator is used mainly for surface network modeling and optimization, but the complex subsurface well system was modeled with this application. This complex simulation model resolves and finds the optimal ICV pressure drop and diameter for each lateral for different inflow-performance conditions, such as different rate-dependent GOR curves at different operational conditions. The model was created as a black-oil model. In each lateral, the flow and pressure drop through the reservoir are determined in the horizontal section, as well as the annular flow between the casing and tubing. Each ICV is represented with a choke model. The primary method for validating a model is to match it to an observed production well test. This validation includes the requirement to represent flow and pressure at different operational conditions in order to predict operational conditions. A nodal analysis of a well model consists basically of two different curves—an inflow curve that represents the flow rate and flowing bottomhole pressure at different conditions and an outflow curve that represents the behavior of the pressure drop at different flow rates through the completion. The intersection of the inflow and outflow curves determines the operational point and is the point that needs to be matched at different operational conditions.