| Skin factor is a dimensionless form of additional pressure drop occurred at oil and gas inflow procedure. The skin factor gained by the well test should be decomposed into several skins by experience formula to find out the mechanical skin due to formation damage. Evidently, the influence of formation damage on different type of completion is not exactly the same. Therefore, a new skin factor model which considered the influence of completion type, permeability anisotropy and damage zone is needed.This paper derived a new skin model through mass conservation d equation, modified Darcy's law and definition of skin factor. This model used dimensionless flow area as integral function, the flow path as integral section. It can basically reflect the additional viscosity pressure drop due to flow path difference and additional inertial pressure drop due to high speed convergent flow. We also derived the flow path of all kinds of completion such as open hole, slotted liner, case perforated and gravel pack. Therefore, we can analyze the influence of anisotropy factor, the damage zone and completion parameter on skin, pointed out that in highly anisotropic formation, choose 180 degree perforated phase and 90 degree perforated direction could gain a skin even smaller than open hole. Theoretically proved that if perforated length is designed(or after acidizing ) through the damage zone, the skin could be greatly decreased.So this innovative model can be use as horizontal productivity forecast, completion parameter optimization and guideline for acidizing technology.Meanwhile, author presented a new FVM theory to solve the completion problem which coupled ordinary flow in the tunnel and seepage flow in porous region. The pressure distribution got form 3D , steady flow , FVM well-completion model are very familiar with the analytical result, which validated the correctness of skin factor model mentioned above. |
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