AAPG Annual Convention and Exhibition

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HC Migration and Trapping in Unconventional Plays


We will show in this presentation a collection of evidence for HC migration at various scales in unconventional plays. This includes spatial variations in fluid properties (API, GOR, H2S) which conform to structure, faults, and depositional facies boundaries, production of higher maturity fluids from low maturity, or immature strata, and production of different fluids from adjacent, or interlaced zones. Mixing and/or interlacing of high maturity and low maturity fluids due to differential migration often results in higher saturation pressure. This can lead to excessive gas production in an oil play or liquids drop out near the well bore in a gas play. Migration distances are estimated to be one to tens of kilometer laterally and hundreds of meters vertically. Traditional sweet spot predictions have been mainly focused on source rock maturity. This may have led to incorrect predictions due to lack of consideration of migration as a factor. Companies who acquired leases based on maturity estimates alone have sometimes found themselves producing more gas than expected, and sometimes even dry gas from rocks currently in the “oil window”. We will also demonstrate that seals are a very important and are a required element for unconventional plays to be successful. Homogeneous shales without sealing intervals will not retain sufficient hydrocarbons, even where maturity, TOC, porosity, and clay content, etc. are favorable. Exploration for unconventional plays therefore also needs to investigate structure, depositional environments and for potential sealing units. In other words, the same evaluation criteria apply to conventional and unconventional plays, just at smaller scales in the latter case. In our examples, we analyzed data from ~ 2 million wells to recognize and demonstrate regional migration patterns in several basins.