Downhole Water Loop-A New Completion Method to Minimize Oil Well Production Watercut In Bottom-water-drive Reservoirs
Authors: Wojtanowicz A.K. , Xu H. 
Published: March 2010

Investigated in this study is a recently invented method to cut back the volume of formation water produced by an oil well from a hydrocarbon reservoir underlain by a water zone. The method involves initial completion of the well inside the water zone, below the oil-water contact (OWC) to install the water loop equipment, which is then separated by a packer from the conventional completion in the oil zone (above the OWC). Below the packer, the water loop installation includes a submersible pump, the upper perforations (water sink), and the lower perforations (water source). The submersible pump drains the formation water around the well from the water sink, and then reinjects the same water back to' the water zone through the distant water source perforations., In principle, the method should increase oil recovery with less (or no) formation water produced at the wellhead. Also, the method gives solution to the environmental problems associated with safe disposal of produced water.

A simulation study was conducted to investigate the hydrodynamic performance of the method to restrain water movement towards oil-producing perforations. The downhole water loop was mathematically modelled using the flow potential distribution generated by two constant-rate sinks (oil and water) and one constant-rate source (water) located. between tne three linear boundaries and the constant-pressure outer radial boundary. The mathematical model was verified using data from studies on water coning. A good match was obtained when the distance between water source and water sink approached zero.

The study reveals that the shape of the dynamic OWC in the well's vicinity can be effectively controlled by the method so that the oil production rates can be two- to four-fold higher than the critical rates obtained when using conventional completions. The method becomes increasingly effective when:the oil production by strong water drive is hindered by water coning;the bottom section of the well (in the water zone) is deviated so that the water source can be set below and aside from the water sink; andthe water zone is thick enough to allow sufficient lateral departure of the water loop without excessive curvature of the bottom section of the well.

Introduction

Several new concepts have been developed recently regarding concurrent and independent production of hydrocarbon and water in a single well. These new stimulation techniques derive from the principle that the local reduction of formation pressure would tender an increase in the well's productivity (1,8). In desorption-type gas reservoir, such as coalbeds and shales having a natural microfracturing system, the removal of water result in dewatering of the fracture system, higher gas saturation, and an increase in the relative permeability to gas. In water -drive oil reservoirs with water coning problems, the removal of water reduces the water flow potential field around the well so that the water come is kept down and below the oil producing performance.(2,8).

Dewatering of coaled methane gas formation has been already successfully applied in field operation.