The Effect of Permeability Stratification in Complete Water-Drive Systems
- Morris Muskat (Gulf Oil Corp.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- December 1950
- Document Type
- Journal Paper
- 349 - 358
- 1950. Original copyright American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Copyright has expired.
- 5.2.1 Phase Behavior and PVT Measurements, 4.1.5 Processing Equipment, 4.1.2 Separation and Treating, 2.4.3 Sand/Solids Control, 5.2 Reservoir Fluid Dynamics, 5.7.2 Recovery Factors
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A theory is presented for calculating the performance history of completewater-drive systems producing from idealized stratified formations. The generalequations are applied to systems where the permeability stratification iseither of the exponential or linear type. Calculations were carried through fordifferent degrees of permeability stratification, but with special emphasis onthe effect of the mobility ratio between the produced oil and the invadingwater on the resultant performance. These results are also expressedgraphically as curves for the initial water breakthrough recovery, for thedifferent degrees of stratification, as a function of the mobility ratio, andof the composition of the produced fluid stream as a function of the cumulativeoil recovery. For several typical cases the latter has also been plotted as afunction of the cumulative oil and water through-flow. The general result isthat when the mobility of the oil is lower than that of the invading water thechannelling tendency resulting from the permeability stratification becomesaggravated as the higher permeability zones become flooded out. Situations ofthis type would obtain when producing low gravity or highly viscous oils.Conversely, if the mobility of the oil is high compared to that of the invadingwater, the flooding of the high permeability zones will lead to a retarding andchoking effect, and the gross bypassing phenomena will be partially suppressed.These conditions would correspond to those of flooding high gravity or lowviscosity oils. A discussion is given of the various basic assumptions made inthe analysis, including that of ignoring the stripping phase of the productionhistory as implied by relative permeability concepts.
The physical ultimate recoveries from oil reservoirs are basicallydetermined and limited by the physical oil displacement processes associatedwith the reservoir producing mechanism. In practice, however, the economicultimate recoveries are further limited by the mobility of the reservoir fluidsand the uniformity and continuity of the producing formation. In fact, it isthe differential depletion between the component parts of the compositereservoir which ultimately determines the total recovery at the time of fieldabandonment.
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