Study on the Profile Control Pilot Test by Microbial after Polymer Floods in Daqing Oilfields
Authors: Cheng Jiecheng , Li wei , Zhang Jingyuan , Wu Junzheng , Yang Zhenyu , Guo Cuiling 
Published: February 2016

In order to further enhance oil recovery of the reservoirs after polymer flooding, two strains of bacterium that could be used on microbial profile modification have been screened. The bacterium were separated from the fluid sample produced within the commercial polymer flooding blocks of Daqing oil-field, and named DT-1 and DT-2. The evaluation of performance showed that these two microorganisms could not only adapt to the special conditions of the reservoirs after polymer flooding, but also could grow well with the in-situ microorganisms. The result of physical simulation core flooding proved that the formation could be plugged perfectly by injecting fermented liquid of DT-1 and DT-2 (the rate of plugging was more than 70%) proceeding the polymer flooding and oil recovery could be improved about 3.9% (OOIP).The microbial profile modification field test has been carried out in Sa-Bei Oil field after having carried out polymer flooding. The result has showed a good effect. After microbial treatment, the injection profile has been changed greatly, which some of the old taking-fluid zones disappeared or others taking 87.2% of the fluid became taking only 25.4% of the fluid and several new zones were taking water. As a result, the incremental oil amount was more 16 tons per day than that before treatment and the water cut has decreased 3.9%. Altogether, the oil production has increased 1300 tons totally. This study has provided a good method for enhancing oil recovery after polymer flooding.

Introduction

After polymer flooding, there is still about 50% OOIP oil remained in the reservoirs. But it has great difficulties in recovering the remaining oil by conventional technologies. The data from core flooding studies, numerical simulation and field tests indicate that after polymer flooding, the remaining oil mainly distribute in low and middle permeable reservoirs while the oil recovery percentage is high for high permeable reservoirs, where the polymer solution can easily breakthrough. Therefore, the reservoir profiles after polymer flooding should be further modified to satisfy the needs of permeability variations in heterogeneous reservoirs.

The agents used for profile modification are usually organic or inorganic compounds. The compound materials are expensive and some of chemical agents are harmful to people's health or pollute the formations, and some of them are dangerous for the operation in the field. The microbial profile modification is an EOR technology that has rapidly developed abroad in recent years for simple process, safety operation, non-pollution to the environment and low cost.

This paper concentrates on the introduction of microbial profile modification field test and its results, which was conducted in Daqing Oilfield.

1. Laboratory Studies and Evaluations on Bacterium Screening

After polymer flooding, there is not only oil, water but also some polymer solution remained in the reservoirs. The microorganisms screened for profile modification, not only can grow up well in complicated conditions of reservoirs with oil, water and polymer solution compound together, but also should have an outstanding capacity of plugging and profile modification to enlarge sweeping efficiency and improve oil recovery.

1.1 Bacterium sources and its separation

A great number of production fluids were sampled from commercial polymer flooding area. With the separation experiments again and again, 234 strains of bacterium were initially selected and were preserved in the nourishing bevel face. Then with further screening, two strains of bacterium were separated which could meet the needs above mentioned and were named DT-1 and DT-2 respectively.

1.2 The shape of screened bacterium for profile modification

DT-1, a kind of threadlike bacterium, can produce considerable spores with diameters of 3~5µm during its growing period. The temperatures suitable for its growing up should be at 32?~45?. A large number of spores can be obtained after DT-1 has been cultivated for about 36 hours. The spores germinate and grow up under certain conditions and come into membranes at last.