Frac-packing has been widely used as an efficient sand control method in Gulf of Mexico fields. For frac-packed wells, rock stability issues within the reservoir are not normally considered when well drawdown levels are established. Instead the emphasis is on how the completion’s integrity can be maintained given that mobile sand is produced. A frac pack can prevent sand from entering the wellbore; however, a skin increase and PI degradation occurring during production is not unusual. Conventionally, PI decline is believed to result from flow-related fines migration or from mechanical failure of completion equipment. This paper presents a case in which theoretical quantification of sand failure around a frac pack provides a viable explanation of field observations. In addition to the skin at the fracture face, PI analysis indicates that additional damage, which contributes to gradually increasing PI degradation, has developed around the fracture. Extensive laboratory core testing has shown that fines are produced only moderately even at high fluid flow rates. However, significant permeability reduction occurs when loading stress increases to a threshold level. A near-wellbore geomechanical model with an embedded fracture has been coupled with a flow model to simulate drawdown and depletion effects on rock stability around the fracture. The placement of a hydraulic fracture during frac-pack operations has been found to have two major effects upon the surrounding reservoir rock. Rock strength is increased at most locations around the fracture, a finding consistent with current industry perceptions. Secondly, certain regions in the vicinity of the fracture tip are weakened as stresses are elevated. Rock starts to fail at a certain level of depletion in either shear or compaction modes, depending upon the rock’s location relative to the fracture and its strength and stress path. These findings demonstrate that rock stability needs to be considered when determining drawdown limitations in sand control completions, in order to avoid unexpected PI degradation.
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