Study On The Integration Simulation Model Of Casing Inside And Outside Gravel-Packing In Horizontal Wells

For unconsolidated sandstone reservoirs, gravel packing technique in horizontal wells not only has good effects, but also reduces the impairment of the production of oil and gas wells and may even increase the production. Current casing outside gravel packing technology in vertical wells has been widely used, but the technology in horizontal wells of unconsolidated sandstone formation is still in the stage of preliminary exploration. In this paper, based on the study of casing inside gravel packing and the technology of casing outside gravel packing in horizontal wells, integration simulation model is proposed, and casing outside gravel packing is conducted in-depth study.As the rock strength parameters are important factors in casing outside gravel packing, a lot of experiential models for the rock strength parameters based on log data and experience have been researched. The time-varying model of rock strength near well is proposed and established, in which the impact of sand production and the production time on rock strength are considered.According to rock strength and working condition, unconsolidated sandstone failure mode has been divided into two modes: tensional frac and plasticity compress. A formation failure mode identification method is especially established, to judge whether the failure mode of the formation under high pressure extrusion is crushing failure or cracks occurred failure. For the compression crushing damage, according to Mohr-Coulomb criterion and the basic theory of plane strain axial symmetry, a method to calculate compaction zone size in high pressure extrusion is deduced, in which the non-uniform azimuthally stress effect on the compaction zone size is considered, and the model can be used to accurately describe the formation of extrusion failure mode after packing.Finally, through the mechanism of packing integration in horizontal well, integration packing is divided into casing outside gravel packing and casing inside gravel packing. A method started on critical velocity of suspended gravel to calculate the minimum construction displacement in casing outside gravel packing is established. Based on all theories in the paper, an integration packing integrated calculation software is developed, which can be used to calculate casing outside compacting zone size and the compacting zone dynamic simulation in integrated gravel packing. The paper provides the basis and conditions for integration gravel packing field application in the future.