Tuesday, November 21, 2017

Enhanced Fracture Treatment Evaluation

Fracture design may be fine-tuned by careful postjob evaluation. This tells whether the job went as planned, and test the validity of the plan and the variables on which it was based. Postfracture evaluation requires a drawdown and buildup test, which indicates fracture skin and whether the actual fracture length and conductivity match those planned. This testing is not a common procedure because operators are usually hesitant to stop production for the 10 to 14 days required for the buildup. But in some fields, the practice becoming more common in a few, select wells. For example, in BP's Ravenspurn South field in the UK sector of the North Sea, an extensive program of data collection and analysis was performed on the first six development wells. This included extensive pre -and - post frac well testing, logging and recording of bottomhole pressures during job execution. The program helped optimization of job design for the remainder of the field, leading to significant reduction in the number of wells required. 

A typical problem is that postreatment transient pressure analysis shows the fracture is shorter than indicated by the volume and leakoff of pumped fluid. There could be several reasons for the disparity. A common reason, however, is that most postfracture evaluation models assume ideal reservoir conditions - homogeneous and isotropic formations, uniform fracture width and conductivity and absence of skin damage.

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