Oil that appears on logs as fresh water—low-resistivity pay—has dogged geoscientists since the dawn of logging. With low oil prices driving the reexploration of mature fields, methods of interpreting low-resistivity pay have proliferated. We examine the causes of low-resistivity pay in sands and then explore the tools and techniques that have been developed to evaluate such frequently bypassed zones. A case study shows how log/core integration helps establish the source of low-resistivity pay in India's Gandhar field.
Our understanding of hydrocarbon reservoirs continues to improve with the addition of every new measurement. That understanding is poised for a quantum leap forward with the introduction of the latest generation of nuclear magnetic resonance imaging tools. These tools make measurements on hydrogen nuclei present in formation fluids. We look at how this technique permits determination of pore size distribution, lithology-free porosity, free-fluid porosity and an estimation of permeability on a continuous log.
A specially designed fluid is the lifeblood of a complex hydraulic fracturing treatment. Pumped into a reservoir at high pressures and flow rates, it creates a conductive crack in the rock that yields a several-fold increase in well productivity. We trace the revolution in fracturing fluid technology that has occurred in the past several years and, through laboratory and field case studies, explore how four recent innovations are helping solve problems that have plagued fracturing operations for decades.
An increasing percentage of oil and gas today comes from marginal fields that are small, complex and difficult to map. One example is the Wandoo field of Western Australia—a shallow, sandstone reservoir obscured by complex structure and overlying layers that generate noise. In Wandoo, clear imaging of the pay zone required a new approach to seismic acquisition, with high-density sampling. This is the story of how a high-density survey works and how it sees detail missed by conventional methods.
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