Field Experience Utilizing High-Density Brines as Completion Fluids

Abstract

Summary This paper presents the results of 2- years experience using high-density brines as completion fluids in fields offshore Texas. This experience has resulted in a number of improvements in field methods of handling and using these fluids in making gravel-packed completions in abnormally pressured wells. Because the required fluid densities have been in the range of 15.0 to 15.6 Ibm/gal (1797 to 1869 kg/m ) and the fluids have cost several hundred dollars per barrel, the cost of lost or contaminated fluid has been a significant factor in carrying out these completions. We have developed our current completion methods in an effort to minimize fluid costs, maintain well control, maximize productivity, and minimize rig time per completion. The methods developed include those for perforation cleaning, gravel packing, solids removal, density control, control of fluid losses, and prevention of crystallization. The results of these methods generally have been successful in controlling completion costs and apparently are successful in providing good sand control and adequate flow efficiencies on the basis of initial test results for about two-thirds of the wells. Introduction Amoco Production Co., as operator for a group consisting of Mobil Oil Corp., Union Oil Co. of California, and Amoco, acquired three adjoining Outer Continental Shelf leases in the May 1974 federal offshore lease sale in what would become the High Island Block A-537 field, The field has been the primary location where we have used high-density brines. This paper describes the basis for using heavy brines in these completions, the plans developed for the completions, our experience in performing them, the resultant evolution of our procedures, and the achieved well productivities, which have confirmed the advantage of using a solids-free completion fluid. The field is located approximately 85 miles (137 km) south-southeast of Galveston, TX, in water depths of 190 to 200 ft (58 to 61 m) in the Gulf of Mexico. Exploratory drilling began in 1974, and a total of five exploratory wells were drilled during 1974–75. The first exploratory well drilled in the field, OCSG-2698 Well No. 1, encountered hydrocarbons in Pleistocene sands while being drilled with 16.5 lbm/gal (1977 kg/m3) mud. The well was cased, and a drillstem test (DST) was made in a 10-ft (3.05-m) perforated interval. The well flowed at rates of 450 to 720 B/D (71.5 to 114 m3/d) oil. The shut-in bottomhole pressure (BHP) was 5.243 psig (36.1 MPa) [a 13.7-lbm/gal (1641 -kg/m3) equivalent] at 7,352 ft (2241 m) TVD. Following this DST, sand had to be washed from the well beginning at a depth 80 ft (24.4 m) above the perforated interval, indicating that sand control would be necessary in wells completed in this field. JPT P. 881^