| Popis: |
The Panna field is a heterogeneous limestone reservoir consisting of a thin oil column overlain by a gas cap and underlain by a water column. The reservoir is coning dominated and the wells show a marked increase in Gas Oil Ratio (GOR) and water cut very early in the production history. Horizontal wells were drilled to minimize drawdown, and hence coning, and maximize recovery. The initial horizontals had openhole completions and displayed a peculiar inflow performance curve that was concave upwards and almost flat at the higher rates. This was thought to be caused by the formation of water sumps at low rates, due to the undulating profile of the drainhole & the low fluid velocities, which resulted in a non-uniform flow contribution along the horizontal. Subsequent wells were completed with a centralized, selectively perforated tubing (tailpipe) installed in the drainhole and it was thought that this would result in a uniform flow contribution along the entire horizontal section and correct the inflow performance curve shape. Analysis of pressure data from the tailpipe wells showed that the tailpipe caused progressively higher drawdown at high rates. However, the flow distribution along the drainhole could not be determined from pressure data alone. A production logging campaign utilizing tractor as the conveyance system had to be aborted due to a) limited coverage of the horizontal section by the tractor and b) operational problems resulting in fishing of the tractor in one of the wells. This campaign was expected to provide an insight into the flow process in the two completions and determine the most optimum one. This case study presents the performance of the various horizontal completions in existence in the field and integrates production and bottom-hole pressure data to explain them. |
