Investigation of Fine Migration, Clay Swelling and Injectivity problem during FAWAG Study in West Malaysia Oil Field
Authors: Osman Adil Mohamed , Halim Nor Hadhirah , Alwi Noraliza , Sedaralit Mohd Faizal , Ibrahim Jamal Mohamad , Hamid Pauziyah Abdul , Ohen Henry A 
Published: March 2015

A number of Malaysian mature oil fields have been and are still under investigation for Enhanced oil Recovery (EOR). This includes Water Alternating Gas (WAG), chemical flooding and Foam assisted WAG. This field is one of the most fields under extensive EOR studies for WAG & FAWAG. Despite the promising recovery factor from EOR application there are always the side effects that accompany these processes which are formation damage and injectivity issues.

A lot experiments studies shown, when a large number of pore volumes of polymer is injected with medium permeability beyond a critical shear rate, a plugging tendency is observed. This plugging is attributed to a damage mechanism called "bridging adsorption" in which stretched polymer macromolecules form numerous bridges across pore throats. At the same time, causes fine migration issue.

In this study, the effects of fines migration, clay swelling and injectivity were investigated in separate core floods studies (one test for fines migration, one test for clays swelling and three for chemical injectivity). For the fines migration study, the core flood test to investigate the critical flow rate of the seawater injection shows fines migration problem as observed from sea water injection of intermediate critical flow rate for fines migration in the core. For clays swelling the permeability reduction test and pH measurement with decreasing salinity indicates a critical salinity much less than the sea water salinity and sea water is the proposed medium for the EOR chemical in this field. Moreover, SEM investigation analysis result shows that most of the damage is due to fine migration caused by the velocity flow rate of the injection sea water.

For injectivity study, core flood tests were conducted with injecting surfactant polymer (SP) solution and with surfactant and polymer individually. The results show that while minimum damage of less than 30% is typically expected in this type of test with permeability resistance factor of less than 3, what was actually obtained in this test is about 95% damage and permeability resistance factor (PRF) is 23 compared to KPI of 3. The results also indicate that incompatibility between the surfactant and polymer could be one of the reasons for permeability decline. This is because while injecting the chemicals separately no serious injectivity issue is observed.

Introduction

EOR studies prior to field application have recently enjoyed global attention due to several reasons including declining oil production below par primary and secondary recovery, high crude oil price and increasing energy demand which is growing at approximately 1.5% per year (Du, K., et al, 2011). Laboratory testing in support of field application is critical to minimize field application failures. This paper addresses possible risk of formation damage due to fine migration, clay swelling and polymer absorption during Foam Assisted Water Alternating Gas (FAWAG) process proposed for the field.

The offshore field is located 170 km away from West- Malaysia land. Currently this field is being considered for enhanced WAG process called Foam assisted Water Alternating Gas (FAWAG). In this process it is proposed to alternate polymer surfactant with gas instead of water. Surfactant is proposed to precede the gas injection, which will generate foam in-situ. Foam so generated along with the polymer is expected to improve the displacement efficiency by virtue of better mobility control, once implemented, This field will be the first such application in Malaysia.