Fracturing Unconsolidated Sand Formations Offshore Gulf of Mexico

Abstract

SPE Members Abstract This paper presents case histories for two offshore Gulf Coast wells completed with hydraulic fracture stimulation treatments followed by gravel pack installation. This completion technology is relatively new to the Gulf Coast area and is being employed to address the unique sand conditions encountered with unconsolidated sandstone reservoirs. Successfully fracturing soft sandstone formations poses different challenges than fracturing hard-rock reservoirs. The tip screenout design technique is used for fracture design to ensure that the fracture width and proppant concentrations are adequate to efficiently connect the reservoir to the wellbore. Downhole pressure measurements and multiple-tracer isotope tagging of fracturing fluids and slurry are used both for on-site design aids and post-job evaluation. The case histories presented demonstrate that hydraulic fracturing of soft sandstones can provide effective stimulation when properly executed. Introduction Problems with severe production decline have hampered the development of reserves in the L-1 sand since discovery. It was while studying ways to improve the recovery from this sand that testing offshore fracturing of soft sandstones was considered. This large oil reservoir exists within the Eugene Island Block 316 lease area located about 80 miles offshore from central Louisiana (Fig. 1). The L-1 sand is located at the top of the Lenticulina section which is early Pliestocene in age. This reservoir has been interpreted as a very fine-grained sandstone deposited as a distal facies in an upper slope environment. The zone is characteristically a low resistivity pay reservoir ranging from 80 ft to 1 70 ft in gross thickness with 40 ft to 1 00 ft of net effective sand. Routine sidewall core analysis has shown the reservoir to be mostly very fine grained, very shaly, silty, and laminated. The L-1 sand appeared as low perm in most of the sidewall cores with permeabilities mostly below 10 md and core porosities ranging from 18% to 21 %. Several of the cores did show the presence of cleaner sand stringers having core permeabilities greater than 1 00 md and core porosities ranging from 24% to 25%. P. 817^