Increase of Accuracy in Determination of Skin-Effect and Perm Thickness Product ForLow Permeability Reservoirs

摘要

Pressure build-up time upon shutting-in a well depends onrnfiltration parameters of formation, increasing with theirrnimpairment. Therefore, incomplete pressure build-up curve forrnlow permeability reservoirs frequently occurs. In this case thernsegment, offsetting by 1.5 of log cycle from derivativernmaximum, is not achieved. Interpretation of such pressurernbuild-up curves, using known programs as Pansystem, Saphir,rnFekete etc., leads to a significant error. This is confirmed byrnskin pressure drop with the absolute values considerablyrnexceeding depression, as well as unreal flow efficiency.rnIn this connection, a method for interpretation of pressurernbuild-up curve has been elaborated, allowing to increasernaccuracy in determination of formation and bottom-hole zonernfiltration parameters. This is achieved by combinedrnconsideration of wellbore storage and prehistory of filtrationrnusing numerical methods. In so doing, knowledge of initiallyrnunknown formation pressure and boundaries, on which it isrnmaintained constant, is not required.rnThe method received wide practical approval for reservoirsrnwith permeability of 0.1-300 mD. The results showed thatrnactual value of perm thickness product, calculated byrnsuggested method, is smaller then by well-known methods.rnThe difference is increasing at short pressure build-up timernand also for reservoirs with low perm thickness product.rnTherefore, the most effect from application of the suggestedrnmethod is achieved while interpretation of pressure build-uprncurve with low perm thickness product. The method has alsornbeen used to estimate efficiency of different stimulationrnmethods for wells, drilling-in and completion methods inrnTatneft JSC fields. Results of interpretation allowed to givernpractical recommendations on selection of most efficientrntechnologies.