Estimation of Reservoir Parameters of Hydrocarbon Bearing Shaley Sand Reservoir Using Well Log Data
Shashi Ranjan Sharma
M. Tech Applied Geology II Year, Department Of Earth Sciences IIT ROORKEE
Well Logging can be defined as the systematic recording of the in wells being drilled or produced to obtain various characteristics of down hole formations. The continuous recording of geophysical data along a borehole against depth is called geophysical well logging. Many geological and geophysical methods have been found satisfactory for locating hydrocarbon but these are indirect methods. They indicate the structural and stratigraphic location, where hydrocarbon might be found. They give no evidence wheter there might be significant accumulation at a depth of one or two mile below the surface of earth. The only method that is available for answering these questions is the exploratory wells. Almost all oil and gas produced today comes from accumulation in the pore spaces of reservoir rocks usually sandstones, limestone or dolomites. The amount of oil or gas contained in a unit volume of the reservoir is the product of its porosity and the hydrocarbon saturation. In addition to the porosity and the hydrocarbon saturation, the volume of the formation containing hydrocarbons is needed in order to estimate total reserves and to determine if the accumulation is commercial, knowledge of thickness and area of the reservoir is needed for the computation of its volume. To evaluate the producibility of a reservoir, it is necessary to know how easily the fluid can flow through the pore system. This property of the formation rock, which depends on the manner in which the pores are interconnected, and is its permeability. The main petrophysical parameters needed to evaluate a reservoir are its porosity, hydrocarbon saturation, thickness and permeability (Schlumberger, 1989). A large number of parameters can now be measured by using different tools. They include resistivity, bulk density, interval transit time, spontaneous potential, natural radioactivity and hydrogen content of the rock. The objective of the present study deals to determine the lithology by using different log responses eg. Gamma logs, self potential logs, density porosity combination and different crossplots, to formulate and choose mathematical transformation equations interrelating logging measurements with individual rock parameters as realistically and judicially as possible and to solve appropriately selected equations to determine all essential geological and reservoir parameters. This integrated study deals with qualitative interpretation of well log data and to bring forth the effective porosity, shale volume, hydrocarbon saturation (movable and residual), and predict the maximum producible zone. This study also includes that, with the change in shaliness, resistivity of formation also changes and we can say, it is not necessary that only high resistivity is the indicator of hydrocarbon i.e. low resistivity can also produce hydrocarbon.