Field Investigation of Effect of Thawing Permafrost Around Wellbores at Prudhoe Bay
Authors: Davies B.E. , Boorman R.D. 
Published: December 2007

This paper was prepared for the 48th Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Las Vegas, Nev., Sept. 30-Oct. 3, 1973. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made.
Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

Abstract
Production of hot oil through conventionally completed wells in the Prudhoe Bay Field will cause thawing of the permafrost around the well-bore. Permafrost in this area is approximately 2,000 ft thick. This paper describes a field experiment conducted by BP Alaska Inc. to investigate whether development of a considerable thaw zone around a well-bore would result in soil subsidence or excessive casing stress. This experiment consisted of circulating hot oil at an inlet temperature of approximately 190 degrees F for 12 months in two differently completed wells through the permafrost interval, to achieve a thaw radius of approximately 11 ft around each well-bore. Casing strains and soil movements were monitored at frequent time intervals. Techniques included surface load cells, wireline logs such as temperature, cement bond, gamma-ray, multiple collar locator and casing inspection logs. Also, frequent surface elevation surveys of wellheads and subsidence rods were made. Radioactive bullets were shot into the formation around one well to measure soil movement. All these techniques are discussed in the paper. The results of the experiment are presented and discussed. Principally, these were that no detectable casing Principally, these were that no detectable casing damage occurred in either of the wells, no significant casing stresses or strains were detected by the techniques used, and that below approximately 650 ft, there is no conclusive evidence of formation movement relative to the casing.

Introduction
Considerable effort has been expended by the oil companies involved in the development of the Prudhoe Bay Field to research the effects of thaw of the permafrost resulting from production of hot oil. The investigations include production of hot oil. The investigations include study of:the geologic nature and mechanical properties of permafrost by obtaining cores of properties of permafrost by obtaining cores of the permafrost and laboratory testing of the core material, and by investigating the mechanical behavior of synthetic permafrost (Reference 2).the thaw associated with oil producing wells (References 3, 4, and 5).the response of the permafrost to thawing and the effect on the well by use of a finite element model for simulation of downdrag forces.
Smith and Clegg, in their presentation to the World Petroleum congress in 1971 (Reference 1), gave a comprehensive summary of the results achieved up to that time.