Optimization of the composition of KCl and KCl+NaCl as a clay/shale stabilizing component in the NDDF for Upper Assam Basin

The drilling fluids are generally maintained at a pressure higher than the formation pressure to stop the invasion of formation fluid into the wellbore. This overbalance pressure is considered as the major cause for inducing formation damage by the invasion of fluids and solids into the formation. According to some researchers, although the depth of invasion and degree of damage is controllable to a certain level by designing the mud on the basis of concentration and particle size of the bridging material and of the pore sizes of the reservoir rock, the invasion of solid and filtrate and corresponding formation damage are inherent to all drilling fluids.

Orthodoxdrilling fluids that are used to drill through water sensitive shale formations may cause a high degree of wellbore instability. The alternate option of Oil Based Mud (OBM) due to their superior shale stabilization properties is also economically and environmentally unfeasible. Due to the challenges with OBM, conventional Water Base Mud (WBM) that have the capability to efficientlydecreasethe shale instability complications have once again comesto substitute the OBM. Water Base Mud (WBM) incorporating KCl is used in the payzones where inhibition is required to limit chemical alteration of shales.

In this work, a clay mineral study was conducted in the rock samples with the help of X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM) photomicrographs and the major clay minerals found to present in the Upper Assam Basin are Smectite, Chlorite, Illite, and Kaolinite; of which Smectite is swelling clay and Illite, Kaolinite and Chlorite are non-swelling clay. Illite and Kaolinite are known as emigrational fines problem clay; and of the clay minerals, Smectite is the least stable and the most susceptible to hydration and diagenetic alteration. So, to counter the damage, an ideal mud for this region must have saline inhibitive filtrate which should not swell the clay envelop around the pay zone particles and should not react with the formation fluid to form insoluble precipitate. In this work, the incorporation of KCl is made in Water based mud system to make it perfect for stabilizing the shale particularly of the Smectite group taking the Bentonite as swelling agent and an effort has been made to optimize the composition of KCl in the Non Damaging Drilling Fluid for Upper Assam Basin to stabilize the clay/shale of the payzone.