Shale Gas/ Oil exploration is getting more and more attention as the existing fields, are in mature stage of production, therefore, time has come for finding the alternate energy resources. Shale gas is one of the future energy resources Therefore, it is essential to address the problem associated with the potential evaluation of shale gas reservoir.
Most of the shale gas reservoirs are fine grained sand or siltstone. It is not possible to find out true potential of reservoirs with the help of conventional logs / methodology. Before the field is even considered for shale gas evaluation, it is essential to acquire TOC and VRO data of the formation. The best way to acquire this data is conventional core or side wall core. Due to time constrained this data is not always acquired or sufficiently sampled. Therefore evaluation of these parameters, TOC and VRO, using the conventional logs is the only option left. With the help of log data, not only the calibrated values at depths can be generated but it gives a continuous log of these properties. These properties when combined with basin modeling studies than it give full hydrocarbon potential volume.
The current study deals with the Cambay Basin where silty sand reservoir has been identified as hydrocarbon bearing. An attempt has been made to determine shale-gas prospectivity of Cambay shale integrating wireline log, mud log, cutting and core data. The affect of gas present in shale reservoir is visible on logs specially neutron, density, acoustic and resistivity. Mud log data also indicates the presence of possible gas bearing zone in study area based upon gas count.
Using a specific workflow, hydrocarbon saturation, porosity and permeability of the reservoir section was computed. The same parameters were used for OGIP calculation & TOC calculation. Thermal Maturity (VRO) computation was done by using log data by making some assumptions. Log derived thermal maturity was calibrated with side wall core VRO in drilled wells. This transform is then used in other wells where core data is not available and undrilled portion of study area for calculation of thermal maturity. Depositional environment classification and facies analysis was done with the help of log data by using neural network technique. The techniques have demonstrated the methodology for shale gas potential evaluation and can be used for different reservoirs.