Abstract

Polymer gels used for shutting off unwanted water in producing oil wells are certainly no stranger to the Arbuckle dolomite formation in Kansas, but in years past, they have delivered short-lived results and have been only marginally successful.In November 1997, that all changed after a unique design strategy utilizing proven polymer gel technology caused dramatic increases in oil production that resulted from shutting off a significant volume of water from a well located in the Bemis-Shutts field.Since that time, more than 200 wells have been treated for about 35 different operators with a greater than 95% success rate. Thousands of barrels of incremental oil at each treated well are being realized, and hundreds of thousands to millions of barrels less water are being produced from each treated well, than otherwise would have been produced without the treatment.These treatments are extending, by several years, the economic life of many Arbuckle wells, and are bringing shut-in wells back to life.

This paper will report lessons learned from applying polymer gel water shut off technology to the Arbuckle formation, and present statistical data derived from a detailed database that has been maintained throughout the project.In addition to using the database as a tool to quantify results and further improve job performance, it is also being used to improve the predictability of response to treatment.Post-treatment oil and water production performance and treatment longevity will be compared to several variables like polymer gel treatment volume and injection pressure.The paper will also discuss how polymer injectivity and post-treatment well performance changes from place to place within the Arbuckle formation.Finally, treatment economics including job cost, payout time, revenue gain from increased oil and decreased water production, and return on investment will be presented.

Introduction

Since the 1910's, several billion barrels of oil have been produced from the Central Kansas Uplift (CKU), primarily from carbonate reservoirs within the Arbuckle and Lansing-Kansas City groups.Most of the Arbuckle reservoirs were drilled prior to 1955, and constitute a series of giant and near-giant oil fields.It is estimated that Arbuckle reservoirs in Kansas have produced about 2.2 billion barrels of oil, representing about 36% of total Kansas oil production to date.About 69% (1.63 billion barrels) of all Arbuckle oil has been produced from only 10 counties located on the CKU. Although the Arbuckle has been a prolific producing interval since 1917, annual production peaked in the early 1950's at more than 68 million barrels and has declined to approximately 12 million barrels per year in 2002.Today, Arbuckle wells can be described as "strippers" with over 90% of wells producing less than 5 barrels of oil per day with oil cuts ranging from 0.5 to 1.0%. Obviously, the economics of operating these wells are very sensitive to oil prices.[1]

Arbuckle Geology and Producing Mechanism

The Arbuckle formation is present in most areas of Kansas, but the majority of work presented in this report has been conducted on the CKU in prolific fields including Bemis-Shutts, Cooper, Emmeran, Morel, Riffe, and Marcotte, to name a few.These fields are located mostly in Ellis, Graham, Rooks, Barton, Russell and Stafford counties.Most of the treated wells are contained in the elliptical-shaped area bounded in red on the map in Figure 1.The Arbuckle has been described by Franseen, et-al as a fracture-controlled karstic shallow-shelf dolomite reservoir with porosity and permeability influenced by basement structural patterns and subaerial exposure.Weathering and secondary dissolution of the upper Arbuckle beds during subaerial exposure combined with the process of dolomitization is believed to have significantly enhanced porosity and permeability, and created petroleum reservoirs in these strata on structural highs.Core reports indicate that the dolomite Arbuckle matrix can have a sucrosic texture with permeability as high as 1,000 to 1,500 md, and porosity in excess of 20%.

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