Abstract

In complex and unpredictable geological formations safe and economical drilling for exploration of hydrocarbons may prove to be difficult at times. This is true if the in-situ formation pressures are unknown or have sudden high pressure zones. Therefore, an accurate knowledge of formation pressure is essential to reduce the well complications. This study studies and predicts the in- situ state of pore pressure distribution in a field of Tripura-Cachar area. The Tripura-Cachar fold belt of Assam Arakan basin is well known for high pressure in NE of India. The exploration activities have been confined mostly to the shallower prospects, whereas deeper prospects are still unexplored mainly because of abnormal high pressure. High pressure creates unwanted problems in successful drilling, testing and completion of a well. In addition to difficulties in designing of proper mud and casing policy, high pressure environment may also create problems in recording of OH log data from the logging tools, as these tools are designed to operate within a fixed range of temperature and pressure values. In the present study, a continuous pore pressure gradient, fracture gradient, over burden gradient and temperature gradient data have been generated through well logs and Bottom Hole Temperature (BHT) data for over 11 wells of Agartala Dome field of Tripura Asset. Out of the 11 studied wells, four wells have been penetrated in the Lower Bhuban formation. Basic log data of Gamma Ray (GR), Density (RHOB) and Sonic Travel Time (DT) have been used for computing pore pressure, fracture pressure and over burden pressure gradients. The computed pore pressure gradient was validated with formation pressure data such as MDT etc. whereas, Fracture Gradient (FG) was validated with LOT (Leak-Off Test) data. The estimated pore pressure gradient was used for generating map for high pressure distribution over the field. Through the map, High Pressure (HP) trend was analysed to predict HP Formation in Agartala Dome field.