Abstract

Historically, hydraulic-fracture stimulation of zones with directly underlying waters has not been considered a practical method for improved oil recovery. This was because the stimulation treatment could result in water cuts from 90 to 100%.

Many of the oil and gas reservoirs in the Khanty-Mansiisky region in western Siberia have production zones that fall into this scenario. The zones contain high-permeability streaks of mobile water and have water-bearing layers above and/or below the producing zone. When a hydraulic-fracturing treatment is performed on such production zones, unintentional stimulation of the adjacent water-bearing layers occurs. As a result, high water production is observed from the high-permeability streaks of water or the adjacent water-bearing layers. Over a period of time, those wells will continue to lose hydrocarbon production rate, while the water cut continues to increase. Water separation and disposal of the produced water is expensive and not always successful.

However, using recent technology advances, the hydraulic-fracture stimulation of such zones has now been shown to be an effective way to stimulate and produce the mature oil and gas fields of the Khanty-Mansiisky region in western Siberia. This method incorporates the inclusion of a hydrophobically modified, water-soluble polymer (HMWSP) with the hydraulic-fracture stimulation fluid. Using this technology, typical water cuts have been reduced from ~86% to ~30%. This paper presents the introduction, implementation, and analysis of two pilot projects that were performed in the Khanty-Mansiisky region located in the middle of western Siberia in 2005 and 2007. (1) The HMWSP technology implementation, (2) lessons learned, (3) production and job-data analysis, and (4) results and recommendations for the selection of candidates and successful implementation of the new HMWSP technology in the western Siberian fields are discussed.

Introduction

The Ust-Vakh area is the boundary area of the largest oilfield of western Siberia, the Samotlor oilfield, which has been developed since 1969. Field development of the Ust-Vakh area first took place from 1987-1991 when the first 10 wildcat wells were drilled. The first propped fracture stimulation treatment was performed in March of 1992.

The most difficult problem with respect to the Ust-Vakh field development and exploration is that the only zone that produces only oil is the upper part of the formation called AV1(1–2) and AV1(3), and that there is only a "weak" barrier layer below oil-saturated zones. Hence, the fractures created by hydraulic fracturing treatments on that formation are unlikely to stay contained in the oil-saturated zone and usually break into the water-bearing zones; also, this results in high water-cut percent in production. Several attempts, such as pump-rate decrease, gel-loading decrease, linear-fluid usage on minifrac, combined pad usage, etc., were made to change the fracture design to help avoid fracture growth into water-saturated zones. When all measures applied were unsuccessful, it was then decided to implement the new HMWSP technology. This paper describes treatments with application of HMWSP technology. During Phase I of the HMWSP project (2005-2006), four treatments were performed. Phase II of the pilot project consisted of an additional four treatments that were performed in 2007. This paper discusses the treatments and the knowledge gained.

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