An Integrated Reservoir Simulation-Geomechanical Study on Feasibility of CO2 Storage in M4 Carbonate Reservoir, Malaysia
Authors: Masoudi Rahim , Jalil M. Azran Abd. , Press David John , Lee Kwang-Ho , Phuat Tan Chee , Anis Leo , Darman Nasir B. , Othman Mohamad 
Published: March 2015

Abstract
The M4 Field is located north of Central Luconia Province in the Sarawak Basin, East Malaysia. The reservoir is approximately 2000 m below sea-level where the water depth is approximately 120m. An integrated geomechanical study for CO2 geological storage has been conducted to evaluate the feasibility of injecting and storing CO2 in the M4 depleted carbonate gas reservoir. The storage feasibility of M4 reservoir is impacted by interaction of the reservoir rock with carbonic acid formed by dissolution of injected CO2 in the water which has risen close to the cap-rock. The geomechanical study needs to assess the risk of CO2 leakage from the reservoir due to degradation of the integrity of the cap-rock by the injection operations, and interaction of the injected CO2 and carbonic acid with the cap and reservoir rocks.
A scope of work incorporating data review and integration, downhole log and image interpretation, 1-D in-situ stress and pore pressure analyses, rock property determination and 3-D coupled reservoir geomechanical modeling was conducted. In addition, laboratory rock mechanics tests and petrophysical measurements were conducted on core samples before and after injection of CO2 saturated brine solution, and the results were used to develop material strength, elastic and petrophysical property degradation models due to carbonic acid-carbonate interaction. A coupled geomechanical modeling was subsequently performed, which incorporates reservoir pressure and CO2 saturation from dynamic simulation, and subsequent changes in effective stress and the associated changes in porosity and permeability are calculated by a geomechanical modeler which were then passed back to the dynamic reservoir simulation. In addition, modifications were also made to geomechanical and petrophysical rock properties based on the carbonic acid-carbonate interaction degradation models.
The paper describes the staged works from 1-D Mechanical Earth Model construction to comprehensive laboratory rock mechanics testing, 3-D geomechanical model construction, pre-production stress modeling and various injection scenario predictions. Examples of key results and utilization of the results and findings from the geomechanical study to develop recommendations for optimizing the CO2 injection and storage in the M4 Field in order to achieve optimal geological storage management and direct cost savings will be presented and discussed.

Introduction
Along with capacity and injectivity of CO2, containment is a primary function in geological storage performance. Controlling the trapping of CO2 in the subsurface, i.e. storage containment, is of fundamental importance for safe geological storage of CO2. Rock formations can be impervious enough to act as flow barriers to CO2 over geological periods of time. Delineating such a seal, safeguarding its integrity under operational conditions, and verifying its isolation effectiveness are key objectives in achieving a successful CO2 storage project.