Field Implications from Full-Scale Sand Production Experiments

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Abstract During 1992 and 1993, Shell (SIEP), British Petroleum (Sunbury), Elf Aquitaine and Schlumberger Perforating & Testing performed multiple-shot experiments on large blocks of Castlegate sandstone to evaluate sand production versus confining stresses, flow rate and fluid type. Sand production and flow rates were measured from each quadrant. A video probe was used to view the perforations during different stages of the test. Evaluation of the test data plus observation of the perforations and video probe pictures suggest the following conclusions for weak but consolidated rocks:–Removal of comminuted sand debris from the perforation tunnel is difficult with typical oilfield flow rates prior to the onset of water production.–Stable hemispherical arches may form at the wellbore/tunnel interface, reducing sand production.–Multiple perforations result in variable flow and sand production rates.–Sand production in open perforations is dominated by–an initial sand production transient from perforation generated "comminuted" sand within the perforation tunnel. - failure of the perforation tunnel from pressure depletion or excessive drawdown–onset of water production.–Sand production in open perforations from erosion is not significantly affected by typical oilfield flow rates or seepage forces.–Perforation orientation affects sand production rate. Results of these experiments are presented along with implications for sand control and sand prevention. Castlegate sandstone is classified as a weak but consolidated rock with unconfined compressive strength (UCS) of about 1400 psi, porosity of 24% and permeability between 500 and 1000 md. Introduction A significant number of weak but consolidated reservoirs exists throughout the world. Past completion practices were conservative and sand control was utilized because of the uncertainty of sand production. Most of these were gravel packed with substantial skins and reduced productivity. A substantial economic gain could be realized with more accurate models of the onset of sand production coupled with optimized perforating systems and processes, thus the motivation for this work. Concurrent with this work, single-shot sand production experiments were being conducted under CEA-11. By definition, these tests are restricted to hydrostatic pressure. a single perforation and finite size. Much useful information is obtained from these experiments; however, information on the behavior of multiple phased perforations is not possible. The laboratory work reported in this paper consisted of two multiple-perforation experiments using large quarried Castlegate sandstone blocks of approximately 25 ft3 (0.7 m3). The tests were conducted in the TerraTek large-block polyaxial stress frame. Details of this equipment are reported in References 3 through 5. Experimental Procedure The experimental steps consisted of 1) block preparation, 2) perforating, 3) flow/sand production and 4) examination of the block. Block Preparation. The quarried blocks measured 27–1/8 *27–1/8*32-in. high (0.69*0.69*0.81 m). A central 4.75-in. vertical borehole was drilled (perpendicular to the bedding planes) using 3% KCl brine solution as the cutting fluid. Each block was saturated under vacuum with 3% KCl and then filtered odorless mineral spirits (OMS) were flushed through the block from the borehole to the block sides until the percentage brine in the outflow was less than 1.5%. Elastomer sealing sheets are used to seal the top and bottom of the block, allowing flow only through the vertical sides. P. 725^