--> Prediction of Seal Failure and Reservoir Breaching in Deep Water


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Prediction of Seal Failure and Reservoir Breaching in Deep Water


A viable prospect with a good potential for hydrocarbon reserves requires four amalgamated components. Hydrocarbon source and the presence of reservoir that receives, contains and delivers the hydrocarbon to the well head. Top seal that is indispensable to keep the hydrocarbon trapped in the reservoir. Last, but not least, is the drillable feasibility of the prospect. The absence of any of the aforementioned criteria can lead to the abandonment of the whole prospect. However, the common known cause of reservoir breaching is seal failure. Some of the seal integrity symptom and prognosis can be foreseen during the prospect generation phase and ahead of spudding the well location. They can be categorized as follows:

  • Symptoms:
  • Subsurface structural failure such as faults,
  • Shallow faults that reach the mud line in deep water,
  • Intrusive salt-sediment interface,
  • Active diapiric salt that impact the mud line topography,
  • Prospect closes against a salt weld, and
  • Rocking basin.
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  • Diagnoses:
  • The presence or lack of seismic velocity reversal vs. depth (top seal);
  • High sand-shale ratio at the objective and lack of highstand sequence;
  • Narrow drilling tolerance window (DTW) where the pore and fracture pressure are in proximity; and
  • The presence of a large hydrocarbon column, which is a double-edged sword.
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    This article shows case histories where stratigraphy, structural setting, reservoir quality, hydrocarbon source, and seismic attributes support a viable prospect prior to drilling. However, upon post-drill, these wells were deemed to be dry holes. A brief diagnostic assessment follows each case based on the above mentioned causes of seal failure will be discussed.

    These issues need to be examined methodically during the process of generating a prospect. Geopressure coupled with sequence stratigraphy and basin modeling can help establish a winning endeavor.