Successful operation of an offshore field relies heavily on a surveillance program to monitor and describe the dynamic status of the wells. Conventionally, such programs consist of a series of shut-in and wrap-up procedures to collect essential buildup/drawdown pressures for inferring the near wellbore status, drainage volume, well productivity index (PI), etc.

Such surveillance programs are complex and expensive. They require long well shut-in periods, which may be infeasible both economically and operationally in certain scenarios. Although a long shut- in may be prohibitive, pressure buildup data from planned or unexpected short shut-ins are often available in offshore fields.

This paper presents an innovative methodology to infer the necessary information from short shut-in data. The main theoretical basis for the new method is the decomposition of the energy dissipation during the pseudosteady-state flow period. By decomposing the energy loss into time dependent and time invariant components, the dynamic status of the well(s) can be described using available plh drawdown (the pressure difference between one-hour shut-in pressure and flowing bottomhole pressure). The new method has been successfully used in offshore fields to:

  • Create the evolution of the well skin and well PIs

  • Estimate the well's drainage volume

  • Detect/confirm aquifer support

  • Pinpoint the well workover/stimulation threshold and timing

  • Assess the work quality of the workover/stimulation

This paper describes the theory and physics behind the methodology and demonstrates its application in an offshore field example.

Keywords:
Drillstem Testing, drawdown, wellbore skin, flow regime, evolution, production rate, surveillance program, energy dissipation, shape factor, average pressure
Subjects:
Formation Evaluation & Management, Drillstem/well testing
Copyright 2018, Society of Petroleum Engineers
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