HP/HT Developments and Infill Drilling

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HP/HT fields are defined as having pressures above 300 F (150 C) and pressures in excess of 10,000 psi (69 MPa). When pressures increase above hydrostatic, the overpressures result in elevated fracture gradients, with the gap between the formation pressures and the fracture gradient reducing, leading to a narrow mud weight window for drilling.

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These narrow mud weight windows lead to challenges when setting the initial casing setting points at the top reservoir, which has resulted in all of the development wells being drilled prior to reservoir production. This strategy  relies on comprehensive reservoir characterisation, as any learnings from a staggered drilling strategy, can not be used to refine reservoir characterisation and well placement for later wells, as in a normal field development strategy.

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Following production, and typically large depletion rates, the pore pressures and the fracture gradients in the reservoir decrease, further narrowing the drilling window, making well design even more challenging for later in-fill wells.

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As the reservoir fracture gradient reduces the fracture gradient and pore pressures in the shale layers or overburden largely remain constant. The leads to narrow or non-existent drilling windows in normally pressured reservoir undergoing depletion, as well as in HP/HT reservoirs.

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Addis & Yassir has global experience of addressing drilling and production challenges, at the field and well scale, of HP/HT and depleting reservoirs for initial drilling and in-fill drilling and completion design. These are mostly in the mature North Sea region and in S.E. Asia.