Rock Mechanics Aspects of Well Productivity in Marginal Sandstone Reservoirs: Problems, Analysis Methods, and Remedial Actions

Abstract

Abstract The paper discusses different mechanisms that may explain field observations of productivity decline. In particular, this work reviews some central issues related to rock mechanical processes that may directly or indirectly result in productivity decline and also possible remediation in sandstone reservoirs. Some emphasis is put on particle plugging of the formation itself, screens and gravel packs, scaling in the near-wellbore region, behind the screen/gravel sand production (including quantification of produced sand volume/damaged zone), filtercake mobilization, near-wellbore rock compaction and effects of water breakthrough on rock properties. All these mechanisms are directly or indirectly linked to rock mechanics aspects through local pore pressure changes and induced deformations of the formation rock. Plugging may further induce rock mechanical failure around the well. Two principles of direct sand control are discussed, i.e. borehole re-enforcement (expandable screens, gravel-packing, propped fracturing, chemical consolidation) and filtering (standalone screens, gravel-packs, frac-packs, pre-packed screens) and their impact on productivity upon reservoir depletion, scaling, sand production, filtercake mobilization and fines migration. Different analyses are used to highlight central mechanisms of productivity alteration and to define design parameters. In particular, chemo-mechanical effects upon water breakthrough are discussed with respect to permeability alteration around the wellbore and scale formation. Further, examples will be given that remedial actions to remove scale and other plugging agents in certain cases may harm the formation mechanical integrity, and result in sand production, rock compaction and productivity decline. An example of a simple laboratory test to quantify such loss of rock integrity will be given. The work demonstrates how rock mechanical analysis may guide the selection of completion method, and how proper diagnosis of well performance and formation integrity may guide the selection and design of remedial actions.