Sand Control by Application of Special Fluids and Techniques in a Shallow Sand, Offshore, Louisiana: A Case History

Abstract

Abstract Chevron U.S.A. Inc. began development of the unconsolidated 5300′ Sand Reservoir in Main Pass Block 69 Field, Offshore, Louisiana, in 1956. Major development began in 1961. Subsequently 15 wells were completed in the Sand. Some type of sand control has been implemented in each well. Prior to July, 1969, a period that includes 11 of the 15 wells, all were completed inside casing with aqueous fluids but with various types of sand control. The sand control measures included: gravel packing, installation of prepacked liners, and various sand consolidation processes. Since further study and tests on the 5300′ Sand in July, 1969, a different approach to overall completion of wells was implemented. This approach consisted of making open hole gravel pack completions using oil continuous fluids at all times. The 4 most recent wells were completed using oil-continuous muds. Three of the 4 were single-zone producers completed in open hole. The other was an inside-casing pack done because the 5300′ Sand was the uppermost sand in a dual completion. Figure 1 shows the location of the Main Pass Block 69 Field some 85 miles southeast of New Orleans. The 5300′ Sand Reservoir at Main Pass Block 69 is a highly unconsolidated miocene age sand containing an abundant assortment of kaolinite, mixed layer clays, and mica (5-11%). Logs and core data indicate an average quality sand having a typical air permeability of 135 md and porosity of 32.4%. The reservoir is a domal structural trap limited by a water level at the base of the structure and a fault upstructure. Structural relief is about 100′. The main 5300′ Sand is relatively uniform in thickness. One well in a separate fault block has produced from a lower 5300′ Sand section which is different in appearance on electric logs and not connected with the main sand. Some upstructure 5300′ Sand wells appear to contain gas. Oil reserves in the 5300′ Sand are considered significant. Water depth is some 25 feet but because of the unstable ocean floor a specific rig is used and is costly. Figure 2 shows the type rig used in this field beside a typical well cluster. Figure 3 shows an old style production platform. Substantial oil reserves are required to justify new wells, especially for a single-zone producer in the 5300′ Sand. The 5300′ Sand is the uppermost oil reservoir in the field and an open hold completion as the top sand of a dual is not considered feasible. Ten of 11 completions in the 5300′ Sand from the first well in 1956 to 1969 were economically unsuccessful. The one successful well produced from a lower 5300′ Sand section in another fault block. This sand is not considered a part of the subject 5300′ zone. Each well was completed inside casing with some means of sand control, all were subjected to aqueous fluids during completion, and almost every one was treated with acid in an attempt to initiate production shortly after being marginally completed. Beginning in July, 1969, with oil production demand increasing, 4 more wells were subsequently completed by gravel packing, 3 in open-hole, using oil-continuous fluids exclusively. The 3 open-hole completions exhibited high initial producing rates. One has continued to produce at sustained rates and one other has produced erratically with apparent mechanical problems. The third open-hole completion was unexpectedly dry gas and has declined in production due to as yet unknown mechanical factors or pressure depletion. The one inside-casing pack did not potential at high rate but production has been stable at a low rate of decline from initial. This paper describes the 5300′ Sand and reviews evolution of the sand control and completion fluids program up to the present time. Field and laboratory test results are presented along with details of individual well completion methods. Sand control design and mechanics are also discussed. Performance of the four newer wells is presented graphically to illustrate the initial production rates and subsequent change with time.