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This paper extends Tiab's Direct Synthesis technique 1,2 for interpreting the behavior of the pressure and pressure derivative data of a well intersected by a finite conductivity hydraulic fracture. In this technique log-log plots of pressure and pressure derivative data of a pressure drawdown or pressure buildup test are analyzed without using the type-curve matching or regression procedures. A log-log plot of pressure and pressure derivative versus test time for a fractured well in a closed system may reveal the presence of several straight lines corresponding to different flow regimes; bilinear flow, linear flow, infinite-acting radial flow, and pseudo-steady state flow. The slopes and points of intersection of these straight lines are unique and therefore can be used to calculate several well, reservoir and fracture parameters: permeability, skin factor, wellbore storage coefficient, fracture conductivity, half-fracture length, and drainage area. It is found that equations corresponding to the points of intersection are very useful in checking on the parameters obtained from the slopes, when the pressure derivative curve is not smooth. A new equation is derived for calculating (a) the half-fracture length in the absence of the linear flow regime straight line of slope 0.5 such as in the case of low conductivity fracture, (b) the fracture conductivity in the absence of the bi-linear flow line of slope 0.25, and (c) the skin factor in the absence of the infinite acting radial flow line such as in the case of a short test.

TX 75083-3836 U.S.A., fax 01-972-952-9435. AbstractPressure-transient analysis for gas wells has a great importance in the oil and gas Industry. Transient pressure responses of unfractured and hydraulically fractured gas wells may be affected by non-Darcy flow near the wellbore, such important effect needs to be taken into account when estimating reservoir and well parameters. An additional problem encountered in gas wells test analysis is the presence of the rate-dependent skin, which requires a search for another parameter (non-Darcy flow coefficient).Several tests are performed in order to measure the deliverability of gas wells and to describe reservoir performance. Such specific tests as flow after flow, isochronal and modified isochronal were initially designed to obtain the absolute open flow potential of a well, however, the use of these tests has been extended to obtain additional information from the reservoir. Drawdown tests are focused in obtaining such data as wellbore storage, reservoir transmissivity, skin factor, flow efficiency and system geometry. Buildup tests lead us to the average pressure of the reservoir, however, proper analysis of buildup test provides values of permeability, wellbore storage and apparent skin factor. Buildup and drawdown tests are currently analyzed using type-curve matching procedures, which involves trial and error and conventional techniques.Pseudopressure concept, which was used in this study, has shown to provide sufficient engineering accuracy in dealing with gas well test data. This study utilizes characteristic points, intersection and lines found on the pseudopressure and pseudopressure derivative plot to obtain fracture length, fracture conductivity, skin factor and reservoir permeability.It was found that changing the non-Darcy factor, D, the shape of the pseudo-pressure curve varies from the original gas curve shape at D=0, which implies that an additional skin effect is added at high rates. On the other hand, the pseudopressure derivative curve remains on its original shape, then, in spite of increasing non-Darcy effect factor, D, the pseudopressure derivative curve is not affected by this additional skin effect added to the system because of the non-Darcy flow effect. The interpretation technique was successfully tested with simulated and field examples.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractNumerous waterflooding projects are under way throughout the world for increased recovery. Water injection tests of oil zones are frequently undertaken during the planning phase of waterfloods. Analysis of the bottomhole pressure data recorded during these tests not only provides similar information to that obtained from production tests concerning the well and the reservoir characteristics but also allows the mobility ratio between the injected and resident fluids to be determined.Conventionally, pressure fall-off test data is analyzed using semilog plot of bottomhole pressure versus time. This paper is the extension of the Tiab's Direct Synthesis Technique 10-15 to pressure injection and Fall-off tests in water injection wells.Direct synthesis is a transient pressure analysis technique [10][11][12][13][14][15] , which uses log-log plot of pressure and pressure derivative vs. time. Thus, different straight line portions indicating different flow regions are directly analyzed. Direct synthesis is very useful in conditions of short and early time pressure data missing tests. It also verifies the results since it uses more than one equation for the estimation of reservoir parameters such as permeability, wellbore storage coefficient, and skin factor.Finally, field examples of pressure falloff analysis are presented to illustrate use the direct synthesis and results are compared with those from type curves and conventional semilog analysis.

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