Well Screening Criteria For Water Shut-Off Polymer Gel Injection In Carbonate Medium

Abstract

High water production in oil fields is one of the major difficulties for the petroleum industry, as reservoirs become mature. Costs of lifting, handling, separation and disposal of large amounts of produced water; environmental concerns about this water; increased corrosion rates; higher tendency for emulsion; and, scale formation are among the main problems due to water production which often decrease the economic life of a well. Therefore, there is a need to reduce excessive water production. WSO polymer gel injection is a successful method for naturally fractured reservoirs which generally exhibits extreme water cut values. Gels are used in carbonate reservoirs that are dominated by secondary porosity features. This technology will preferentially flow into these features and selectively reduce permeability to water. Success of the application is based on the proper selection of the wells. Currently, gel polymer treatments have an 85-90% success rate in reducing water production and, in many cases, increasing oil production. Gel polymer systems have a penetration property greater than the mechanical methods and cement to provide a deeper barrier against the excess water. Also, plugging due to gel polymers can be removed unlike physical cement plugging which leads to a permanent plug in the porous media. The residual oil cannot be produced from the treated region by cementing method after decreasing of excess water production. The production well treatment involves injection of the gellant into the fractures or high permeability zones that produces a lot of water, thereby reducing oil production. This application not only improves draw-down from the productive zones; but, it also reduces or eliminates the costs associated with the produced water. Candidate Field for WSO application is located in southeastern Turkey which is an anticline structure. The field was discovered in January 1990 and has been on production since 1990. The structural contour map top of D formation is given in Figure.1. The field is a typical carbonate reservoir with primary drive mechanism of bottom water drive. Four formation (Zone-A,B,C and D) are oil bearing throughout the field. Zone-A is dominantly mud-stone. The formation is not expected to have matrix porosity or inter-granular porosity. Accordingly they can act as seal. Fracture porosity is present but limited, mostly in microfracture type and adds limited reserve potential when compared to the reserves created by matrix and intergranular porosity. However, permeability created by fractures is potentially very high. Zone-B is an organic rich limestone and may also act as a seal. Zone-C is a limestone. Upper part of C formation (K-C member) is also reservoir (in quality) with its porosity and permeability values. Zone-D is a limestone-dolomite formation. Zone-D which has a good secondary porosity developed by fresh water leaching and dolomitization.