Application Of Measurement While Drilling In A Shallow, Highly Deviated Drilling Program

Abstract

Abstract In choosing a survey system for a directional drilling project, consideration must be given to the production penalties associated with an off-target wellbore as well as to the simple comparison of survey costs. Wellbore position accuracy requirements for Esso Resources' Norman Wells Expansion Project Drilling Program have resulted in the choice of Measurement While Drilling (MWD) as the primary surveying system. The accuracy achieved at Norman Wells using an MWD system is the product of many factors. In addition to tool design and calibration, the operating and data check procedures are fundamental to achieving the required accuracy in the severe magnetic environment at Norman Wells. Introduction Scope of Norman Wells Drilling Program Esso Resources Canada Limited is currently undertaking a major expansion project of the Norman Wells oil field. This field is located in the Northwest Territories on the Mackenzie River, 145 km south of the Arctic Circle (Fig. 1). The expansion project includes drilling approximately 162 wells between July 1982 and April 1985. The wells are drilled from mainland and natural island locations and from six artificial islands in the Mackenzie River (Fig. 2). Seventy-eight per cent of the project wells are directionally drilled to reach reservoir targets under the Mackenzie River. As of March 31, 1984, 100 of the wells have been drilled. The unique circumstances at Norman Wells demand a sophisticated directional program. The wells are relatively shallow with true vertical depths to the top of the producing zone ranging from 335 m in the mainland area to 490 m at the downdip end of the reservoir. Horizontal displacements to targets extend up to 750 m from the surface locations. Small targets and the requirement for the wellbore to be as vertical as possible through the producing zone have required the use of S-curve well profiles with rapid build and drop rates. Directional wells have been divided into three types (based on displacement) as illustrated in Figure 3. Type 1 wells have displacements less than 270 m, Type 2 wells range from 271 to 550 m and Type 3 wells reach targets up to 750 m from the surface locations. All directional wells are kicked off between 30 m and 50 m and angle is built at a programmed rate of 8 degrees/ 30 m. Maximum angles of 50 degrees, 60 degrees and 70 degrees to Well Types 1, 2 and 3 (respectively) are reached and held. The wells are then dropped into the targets at rates of 4 degrees/ 30 m. Figure 3 illustrates three wells that were drilled fromartificial island locations in early 1984. Target Accuracy Requirements The choice of a survey system to use for wells of this type is dictated largely by the requirement for accuracy. Accurate positioning of wellbores to hit the relatively small targets is important because of the particular nature of the Norman Wells reservoir. Hydrocarbons at Norman Wells are pooled in the Devonian limestone reef complex called the Kee Scarp.