An Engineered Approach to Combating Drilling Problems In the Ricinus Area

Abstract

Abstract Drilling in the Ricinus-Strachan area of southern Alberta has proven to be very expensive particularly when wells are located in what is referred to as the "disturbed belt". Wells drilled within the disturbed belt experience hole sloughing due to unstable shales, and deviation problems due to abrupt changes in formation dip angle and direction. These in turn are a result of extensive faulting in the area. This paper presents data from wells drilled by Mobil Oil Canada, Ltd in the Ricinus area. It discusses the major drilling problems encountered and outlines the development of engineering research and programming to overcome or minimize these problems. Included in the discussion of a fully programmed well are such items as: researching the area, pre-well planning, drilling fluid selection, surface hole drilling, lithology logs, and deviation problems and control. Comparisons of penetration rates with air, fresh water and invert drilling fluids are presented and discussed. Introduction THIS PAPER is presented in three basic sections. The first section is a general review of Mobil's drilling in the area, with discussion regarding some of the problems encountered. The second section discusses the basic drilling problems in the area, relating problems from specific wells, and presenting dipmeter and directional data. The third section of the paper presents a sequence of events suggested as a basis for well programming in the Ricinus area) and discusses the use of various drilling aids to increase pentration rates. History Of Mobil's Drilling In The Ricinus Area Mobil have drilled three Leduc tests, and five Cardium tests in the Ricinus area. The first well spudded in February 1969, and the eighth well reached FTD in January 1970. The Leduc tests are referred to as wells 1, 2 and 3; the Cardium tests are designated as wells 4 to 8. Figure 1 presents the projected eastern boundary of the disturbed belt. The Mobil wells are listed numerically in the order they were drilled with a brief description pointing out some of the problems encountered. Due to the confidential nature of the wells, drilling information is limited to zones above the objective horizons. Wells 3, 5, 6, 7 and 8 were drilled concurrently Figure 1A presents a strategraphic column for geological formations in the Ricinus area. This well was the first deep test for Mobil in the Ricinus area. Figure 1B presents drilling data for this well. Fifteen-inch hole was drilled to 1425 ft, and 10 ', in casing set and cemented to surface. Below surface casing, 8 ' -in. hole was drilled using an extended gel system with ‘polymer additives’. Mud weight was controlled by the use of desilters. As the drilling curves indicate, no problems were encountered with the hole until 10,200 ft, at which point a shock sub twisted off. Subsequent fishing attempts were unsuccessful, and eventually the hole was sidetracked around the fish, with loss of 12 days due to fishing and sidetracking: Drilling from 9100 ft to intermediate depth (at approximately- 13,000 ft) encountered 107 hours of lost time due to hole problems.