Browsing by Subject "Petrophysical"
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Item Correlating petrophysical and flood performance in the Levelland slaughter field(2005-05) Watson, Marshall C.; Lawal, Akanni S. L.; Heinze, Lloyd R.The Levelland and Slaughter fields combined have produced over 1.6 billion bbls from 1937 to date from 6000 wells and currently produce 6% of the oil in Texas. Most of the field is under water and CO2 flood operations. This project investigates reservoir and petrophysical characteristics of various areas in the Levelland Slaughter field in order to assess relation to performance of secondary and tertiary recovery. The benefits would be to use this relationship to identify depositional environment/facies where little to no core data exists. In areas where no flood has been installed, the relationships developed herein could assist in the ability to predict flood recovery and the method of development. The Levelland Slaughter field is similar to several other ramp type, carbonate fields in the Permian Basin. Results once applied and proved successful in the Levelland Slaughter field not only could be applied to many other fields in the Permian Basin, but also to similar oil reservoirs all over the world. The first objective was to divide the field into areas of like depositional environments. This entailed identifying depositional environments via log, core and production analysis. The objective is to integrate geology and production into the study to ascertain whether like data can be considered, especially in an east west sequence across Levelland Slaughter. There are three depositional environments at Levelland Slaughter as follows; shelf with shoals, lagoonal and intertidal/near shore. Once subdivided, relationships between petrophysical properties and secondary recovery rates are developed utilizing Lucia’s rock fabric classification and production plot methods demonstrated by Reza Fassihi of BP. Fassihi demonstrated the method of plotting water cut against fractional secondary oil recovered enabled one to derive the matrix/fracture flow and storage capacity relationships. Based on curves developed by Fassihi, one can conclude there is little to no natural fracturing in the reservoirs in the Levelland Slaughter field. Lucia demonstrated that by plotting porosity against permeability in carbonate reservoirs, one could derive the type of rock fabric and detect facies changes. Net pay for primary and secondary recovery can be different and are dependent primarily on permeability and water saturation. Water saturation varies within the pay zone in lower permeability reservoir rock. Below a given permeability, water saturation increases and become movable. In consideration of the fore going, a typical Levelland well in the 1950’s produced water free, but later, prior to waterflooding, produces 20 to 50% water cut. For secondary waterflood recovery considerations, a critical water saturation exist where an oil bank does not develop, thus resulting in prolong recovery periods or little to no recovery from that particular reservoir rock. From the Lucia classification and Fassihi plots, it appears that most of the rock fabrics are similar and only differ in permeability. This is possibly due to anhydrite inclusion that was deposited in the more permeable rock, thus leaving the lower permeability mudstone porosity intact. Some localized areas could have improved reservoir due to subtle changes in elevation. These elevation changes are critical in the western area because small sea level changes caused substantial areas to go from subtidal to intertidal to supratidal/mud flats. Each of the fore mentioned steps resulting in a reduction in reservoir quality due to salt precipitation or anhydrite inclusions. This does not apply to shoal areas, located at shelf margins, because they were never supratidal, thus there are no evaporates. Thus the higher permeability rock demonstrates higher primary recoveries as well as much greater Secondary to Primary ratios (S:P).Item Correlating petrophysical and flood performance in the levelland slaughter field(Texas Tech University, 2008-05) Watson, Marshall C.; Lawal, Akanni S. L.; Heinze, Lloyd R.The Levelland and Slaughter fields combined have produced over 1.6 billion bbls from 1937 to date from 6000 wells and currently produce 6% of the oil in Texas. Most of the field is under water and CO2 flood operations. This project investigates reservoir and petrophysical characteristics of various areas in the Levelland Slaughter field in order to assess relation to performance of secondary and tertiary recovery. The benefits would be to use this relationship to identify depositional environment/facies where little to no core data exists. In areas where no flood has been installed, the relationships developed herein could assist in the ability to predict flood recovery and the method of development. The Levelland Slaughter field is similar to several other ramp type, carbonate fields in the Permian Basin. Results once applied and proved successful in the Levelland Slaughter field not only could be applied to many other fields in the Permian Basin, but also to similar oil reservoirs all over the world. The first objective was to divide the field into areas of like depositional environments. This entailed identifying depositional environments via log, core and production analysis. The objective is to integrate geology and production into the study to ascertain whether like data can be considered, especially in an east west sequence across Levelland Slaughter. There are three depositional environments at Levelland Slaughter as follows; shelf with shoals, lagoonal and intertidal/near shore. Once subdivided, relationships between petrophysical properties and secondary recovery rates are developed utilizing Lucia’s rock fabric classification and production plot methods demonstrated by Reza Fassihi of BP. Fassihi demonstrated the method of plotting water cut against fractional secondary oil recovered enabled one to derive the matrix/fracture flow and storage capacity relationships. Based on curves developed by Fassihi, one can conclude there is little to no natural fracturing in the reservoirs in the Levelland Slaughter field. Lucia demonstrated that by plotting porosity against permeability in carbonate reservoirs, one could derive the type of rock fabric and detect facies changes. Net pay for primary and secondary recovery can be different and are dependent primarily on permeability and water saturation. Water saturation varies within the pay zone in lower permeability reservoir rock. Below a given permeability, water saturation increases and become movable. In consideration of the fore going, a typical Levelland well in the 1950’s produced water free, but later, prior to waterflooding, produces 20 to 50% water cut. For secondary waterflood recovery considerations, a critical water saturation exist where an oil bank does not develop, thus resulting in prolong recovery periods or little to no recovery from that particular reservoir rock. From the Lucia classification and Fassihi plots, it appears that most of the rock fabrics are similar and only differ in permeability. This is possibly due to anhydrite inclusion that was deposited in the more permeable rock, thus leaving the lower permeability mudstone porosity intact. Some localized areas could have improved reservoir due to subtle changes in elevation. These elevation changes are critical in the western area because small sea level changes caused substantial areas to go from subtidal to intertidal to supratidal/mud flats. Each of the fore mentioned steps resulting in a reduction in reservoir quality due to salt precipitation or anhydrite inclusions. This does not apply to shoal areas, located at shelf margins, because they were never supratidal, thus there are no evaporates. Thus the higher permeability rock demonstrates higher primary recoveries as well as much greater Secondary to Primary ratios (S:P).Item Numerical simulation and interpretation of neutron-induced gamma-ray spectroscopy measurements(2015-12) Ajayi, Oyinkansola Modupe; Torres-Verdín, Carlos; Peters, Ekwere J; Preeg, William E; Schneider, Erich A; Sepehrnoori, KamyNeutron-induced spectroscopy measurements are commonly used to quantify in-situ elemental and mineral compositions of rocks from the processing of measured gamma-ray energy spectra. However, geometrical effects on measured spectroscopy logs, such as thin beds, dipping beds, and deviated well trajectories, can cause shoulder-bed averaging that compromises the assessment of true layer elemental and mineral compositions. Traditional methods of interpreting neutron-induced gamma-ray spectroscopy measurements typically neglect such shoulder-bed averaging effects in the estimation of elemental and mineral compositions. Monte Carlo methods accurately reproduce borehole and formation geometrical effects on spectroscopy measurements but are extremely time consuming and impractical for use in routine interpretation. Reliable measurement interpretation must therefore begin with the development of a fast and accurate forward simulation method that explicitly incorporates measurement physics, borehole, tool, and formation geometry. This dissertation introduces a new algorithm to rapidly simulate elemental and mineral compositions from neutron induced spectroscopy measurements. The algorithm utilizes neutron-gamma ray spatial sensitivity functions to account for environmental and three-dimensional (3D) effects of formation porosity, fluids, dipping beds, thin beds, and arbitrary well trajectories. Simulations assume a logging-while-drilling (LWD) spectroscopy tool furbished with a 14-MeV pulsed-neutron source in the interpretation of gamma ray spectra obtained from high energy inelastic neutron scattering and thermal neutron capture. Results obtained with the rapid simulation method are benchmarked against rigorous Monte Carlo spectroscopy calculations for synthetic conventional and unconventional thinly-bedded reservoirs penetrated by vertical and high angle/horizontal (HA/HZ) wells. The fast simulation method yields calculations in approximately 1e6 the time required by Monte Carlo simulations, with an average difference below 5% between Monte Carlo and fast simulated logs. An inversion-based interpretation method is next introduced to accurately evaluate mineral concentrations from measured spectroscopy elemental logs based on the analytical relationship between elements and minerals through their chemical formulas. In the presence of geometrical effects, spectroscopy elemental and mineral logs are corrected for shoulder-bed averaging by the inclusion of spatial sensitivity maps, which account for such geometrical effects, in the inversion-based interpretation. Calculations are performed with both inelastic and capture gamma-ray spectroscopy measurements which arise from high-energy inelastic neutron scattering and low-energy thermal neutron capture, respectively. This strategy provides two sets of data that can ascertain chemical elements or minerals detectable in only one measurement mode and also independently validates estimated elemental and mineral compositions. In laminated formations, where layer thicknesses are below the vertical resolution of the tool, it is impossible to quantify layer properties with inversion methods. An additional interpretation method based on a new spectroscopy mixing law is therefore developed to estimate elemental and mineral compositions within individual laminae. The new inversion-based interpretation methods are successfully implemented in diverse synthetic and field cases with varying lithology types and well trajectories including vertical and HA/HZ wells. Results show that the developed methods reduce shoulder-bed averaging effects on measured spectroscopy logs by as much as 0.4 yield fraction, 0.17 weight fraction, and 0.34 mineral volume fraction. Finally, a new spectroscopy-based petrophysical interpretation method is introduced that utilizes estimated mineralogy to overcome the common assumption of homogeneous lithology in measured porosity logs, thereby improving the estimation of porosity and water saturation. Inclusion of shoulder-bed averaging effects on spectroscopy mineral logs also increases the accuracy of spectroscopy-based petrophysical interpretation.Item Rapid modeling of LWD nuclear measurements acquired in high-angle and horizontal wells for improved petrophysical and geometrical interpretation(2010-12) Ijasan, Olabode; Torres-Verdín, Carlos; Preeg, William E.Nuclear logging-while-drilling (LWD) measurements acquired in high-angle and horizontal (HA/HZ) wells are influenced by tool, geometrical, and petrophysical effects. Reliable interpretation of petrophysical and geometrical properties from LWD measurements acquired in thinly-bedded formations requires that gamma ray, density, photoelectric (PEF), and neutron measurements be quantitatively integrated with explicit consideration of their effective volume of investigation (EVOI). One of the effects of different tool EVOIs is false gas density-neutron crossovers across thinly-bedded formations. Also, in the presence of tool eccentricity, azimuthally-varying standoff gives rise to an azimuthally-varying effective depth of investigation (EDOI), which introduces errors in the inference of formation dip. Conventional Monte Carlo simulations of nuclear measurements are computationally expensive in reproducing multi-sector LWD responses in HA/HZ wells. Using linear iterative refinement of pre-calculated flux sensitivity functions (FSFs), we introduce a fast method for numerical simulation of LWD nuclear images in the presence of tool eccentricity along any well trajectory. Our investigation of measurement responses from FSFs motivates techniques to explicitly consider the EVOI of LWD nuclear measurements. Simple radial DOI and standoff corrections suffice for interpretation of gamma-gamma images but are inadequate for neutron responses due to larger EVOI and azimuthal aperture. We introduce a new azimuthal deconvolution method of neutron images to improve bed-boundary detection. Neutron DOI varies significantly with porosity, whereby we correct neutron images for penetration length due to changes of porosity along the well trajectory. In addition, we implement a new method of separate linear iterative refinement on neutron thermal group responses to improve the resolution of neutron images across heterogeneous and thinly-bedded formations. The method reduces shoulder-bed effects and false neutron-density gas crossovers. We corroborate these techniques with rigorous Monte Carlo simulations in vertical and deviated wells. A field example of application conclusively indicates that numerical simulation of LWD nuclear measurements is necessary for reliable estimation of petrophysical properties.