Slant Hole Drilling For Natural Gas

Abstract This paper discusses the slant hole project undertaken by Ocelot Industries Ltd. in the Bantry Field located in Southeastern Alberta. Slant hole drilling is not uncommon to Canada; however, it has been primarily used in the heavy oil projects. This paper begins with Ocelot's need for slant hole drilling and the planning of the wells. The major part of the paper discusses the drilling and completion operations and some of the equipment. that was developed as the project progressed. The project commenced September 9, 1981. and the final well finished drilling December 10, 1961. Introduction The project was initiated to develop the Bilk River and Medicine Hat gas reserves under the Tilley "B" Reservoir, a man-made lake approximately 11 1/2 m2 (4 1/2 miles 2) in area and located mainly in Twp IB, Rge 12, W4M (Fig 1). Because the Milk River and Medicine Hat formations are so shallow. 320 and 445 meters true vertical depth (TVD) respectively, the only means of developing the reserves under the lake with adequate departure from shore was by offshore drilling orslant hole drilling. Offshore drilling would have involved constructing islands or drilling from either a barge or ice pad. The cost for this would have been prohibitive, and in the case of the ice pad there was concern for safety and environment. As well, the offshore techniques would require offshore pipelining and wellhead facilities which would enormously complicate any future operations on the wells. The slant hole drilling had several other advantages as well. Multiple wells could be drilled from one wellsite thus reducing the amount of land used. This is particularly important in farmland. The multiwell locations also reduced pipelining and simplified field operations. PROJECT DEVELOPMENT The project involved drilling 24 wells (Fig 1) based on the proper spacing for the area nd the economic and practical limitations of how Ear out the holes could be drilled. The wellswere divided into two types. Type 1 involved drilling 20 wells at 45 ° from surface to TD. Type 2 involved drilling four wells building the angle to 70 ° from 45 °, and then holding angle to TD. The project also included three multiwell pads to evaluate the feasibility of this concept. As slant hole drilling was a relatively new concept, the project was split into two phases. Phase 1 was the test phase and included seven wells: six at 45 °, one at 70 °, and one multi-well pad. Phase 2, which was the balance of the project and was contingent was the balance of the project and was contingent on the success of Phase 1, involved 14 wells at 45 ° and three wells at 70 °. The interwell spacing regulations for the area dictates that where the wellbore intersects the productive formations, it must be 400 meters away from that point in any other well producing from the same formation. Based on this, the targets were picked trying to use as many jutting points along the shoreline for surface locations so as to obtain maximum displacement under the lake (Fig 1).