Browsing by Subject "Sedimentation analysis -- Computer programs"
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Item Computer determination and comparison of volume of clay derived from petrophysical and laboratory analysis(Texas Tech University, 1991-05) Causey, Gary LeeVolume of clay (Vcl) is the most critical parameter to determine in shaly sand analysis. Yet in many areas it is very difficult to determine volume of clay accurately. An overestimation of clay volume can result in effective water saturations (Swe) that are too low, thus making the reservoir look productive. Under-estimation of clay volume can result in effective water saturations that are too high, which can result in the bypassing of a productive zone. The underestimation and overestimation of volume of clay will also effect the calculation of effective porosities used to determine both effective water saturations and net pay. The FORTRAN program SHALE is designed to calculate volume of clay from 14 different petrophysical methods using up to 7 petrophysical logs. In the program, corrections are made for lithology, pressure, mud weight, borehole variations, and bed thickness. In addition, corrections can be made to convert old gamma ray logs to the corresponding API scale. Laboratory determined volumes of clay can be input into the program and each petrophysical volume of clay raethod can be statistically compared so that the user can select the petrophysical volume of clay method that best estimates the true volume of clay. Using the most accurate petrophysical method chosen, SHALE will then derive a linear transform equation that can be used to correct petrophysically derived volumes of clay. Laboratory determined volume of clay data from 7 samples from a lower Miocene deltaic sand in the Malay basin indicates that the gamma ray unconsolidated method was the most accurate in determining volume of clay. Laboratory determined volume of clay from 30 samples from the Cretaceous Olmos shelf sands in Webb County, Texas indicates that the gamma ray unconsolidated method was the most accurate in calculating volume of clay. However, in both the lower Miocene and Olmos sands, all petrophysical methods overestimated the volume of clay and required transforms to better estimate the volume of clay. The overestimation of volume of clay in both the lower Miocene and Cretaceous Olmos sands indicates that it is critical to calibrate petrophysically derived clay volumes to laboratory analysis.Item Petrophysical study of the Glorieta-Clearfork dolomite in the Monahans Field, Ward County, Texas(Texas Tech University, 1992-12) Saha, SouvickCalculation of a reservoir's water saturation using the Archie equation requires the values for cementation exponent (m) and saturation exponent (n). Determination of these two parameters, particularly in carbonate reservoirs, is often difficult. Recently a new method (CAPE) for estimating m and n has been proposed by Maute et al. (1992). In the CAPE (Core Archie Parameter Estimation) method, m and n are determined by minimizing the error between laboratory derived water saturation (Sw (core)) and water saturation calculated by the Archie equation (Sw(Archie)). Because core data are often unavailable, the author substituted dielectric water saturation (Sxo(dielectric)) for core-derived water saturation to determine m and n, and applied the technique to the Glorieta-Clearfork dolomites in the Monahans field, Ward County, Texas. The Permian (Leonardian) Glorieta-Clearfork dolomites in the Monahans field represents an upward-shoaling carbonate platform sequence. The predominant rock type is dolostone and the major mineral constituents are dolomite and anhydrite. Petrographic analysis reveals mainly intercrystalline/intergranular pore geometry with minor vuggy/moldic porosity. In this study the author applied three techniques: (1) non-linear, (2) linear, and (3) m-porosity transform to determine m and n values that minimize the error (errorfunction) between Sxo (dielectric) and Sxo (Archie). Two mporosity transforms were established, but the transform that represented the majority of the data (85%) was used to derive m values. Using data from the Glorieta-Clearfork dolomite in the Monahans field, the non-linear method resulted in the minimum error between Sxo (dielectric) and Sxo (Archie). The m and n values determined by the non-linear and linear methods probably do not represent physical rock characteristics but are only values that minimize the error functions. In contrast, m and n values determined by the mporosity transform method should represent physical attributes of reservoirs such as pore geometry or wettability. In order to further reduce the error between Sxo (dielectric) and Sxo (Archie), m and n were approximated by mathematical functions (polynomial and Fourier series) to model the vertical variation of m and n in the reservoir (variable m and n method). This variable m and n method based on a Fourier series resulted in the greatest errorreduction when compared to the non-linear method. After determining m and n values that result in the minimum error between Sxo (dielectric) and Sxo (Archie), these values can then be used to calculate the water saturation in the uninvaded zone (Sw).