Completion Practices for Prudhoe Bay Wells

Abstract

Introduction The purpose of this paper is to present an overview of the current completion practices for wells in the Eastern Operating Area of the Prudhoe Bay Field. ARCO Oil and Gas Company is the operator of the Eastern half of the Prudhoe Bay Field and SOHIO Petroleum Company operates the Western half. Completion practices in general are similar in both operating areas; however, there are a few significant differences. This paper refers to practices in the ARCO Oil and Gas Company operating area only. With only two and one-half years of production behind us, there is relatively little history on Prudhoe Bay wells, but we have produced a billion barrels of oil in that short time. The operators have drawn on what is believed to be the best available practices in the industry in developing their operating plans for Prudhoe. There is no universally right way to complete all wells, and we believe we are doing what is best for our situation. In this paper we hope to present the perspective of how and why wells are completed the way they are at Prudhoe Bay. The primary consideration in every completion design is the prudent maintenance of the safety and integrity of the well throughout its life. In addition, all completions are designed to accomplish two basic things:To minimize formation damage or maximize well productivity;To provide maximum flexibility over the life of the well.It is through diligent adherence to these goals that the optimum economic benefit is realized from each completed well. This paper describes the basic completion practices utilized at Prudhoe Bay to achieve these goals. The rigors of the Arctic environment are well-known; however, reiterating a few points critical to the design of well equipment may be of benefit. The annual temperature fluctuations range from approximately +80°F in the summer to -60°F in the winter. While the entire completion string is not subjected to these temperature variations, approximately the top 50 feet of the well closely track surface temperatures. The Prudhoe Bay Field is overlain by 2000 feet of permafrost which has a minimum temperature of 14°F near the surface. The temperature then gradually increases to 32°F at the base of the permafrost. The main productive area of the field is 21 miles long and 12 miles across. The Sadlerochit formation is located at approximately 8700' subsea and averages 450 feet in thickness. The gas/oil contact is planar but the oil/water contact varies by more than 100 feet around the field. The bottom hole temperature varies from 185°-235°F across the field and the initial pressure was 4400 psi. SITP may be as high as 3200 psi and flowing temperatures may reach 180°F for a high rate well. The average porosity and permeability of this sandstone reservoir are 23% and 300 md respectively. Initial well capacities range from 5000 to 35000 STBOPD.