WELLBORE INSTABILITY - CASE HISTORIES
- The North-eastern part of India is a tectonically active area, the lithology mostly being shale with the pay zone being fractured granitic basement, having sandstone intercalations. A major operator has drilled approximately 90 wells in this area using the Non-Invasive Fluid additive (predominantly in the payzone). The advantages seen included ability to keep the hole open and stable for longer periods vis-à-vis offset wells, in severe cases there were prolonged fishing operations undertaken and the wells were still stable. In a particular case the wellbore was found to be capable of holding 3000+psi over the predicted hydrostatic window and not exhibit instability. Flow back from the wells was also easier and with higher yield. The wells came online even with only a single application of the compressor, evidencing very low lift off pressures required to clean out the low invasion fluid.
- The East Coast of India can be said to be predominantly Shale and Sandstone with Clay streaks. A major operator has used the additive in this area with noted success. The main advantages brought were pushing the limits of the mud weight window with enhanced wellbore stability. The operator has also used the additive in Deep Water wells. Major advantages seen are fewer differential sticking issues, smooth wellbore, huge reduction in seepage losses. These led to fewer complications and faster drilling. The operator has drilled nearly 21 wells in this area using this additive (predominantly in the payzone).
Western offshore and North-western onshore in India can be considered to comprise of Shale/Carbonate alternations, Shale/Sandstone alternations and Shale/Claystone alternations. The major issues faced are narrow mud weight windows and wellbore instability issues brought about by different permeability/porosity regimes being encountered in the same section. A major operator has drilled nearly 75+ wells in this area using this additive (predominantly in the payzone). Definite improvements seen have been reduction in seepage losses, less stuck pipe, improved mud weight windows, smoother wellbores, easier running casing etc. In some cases, reduction of time spent due to drilling complications have been reduced by as much as 35-40%. The operator has also run this additive with SOBM’s, evidencing its compatibility with both WBM and SOBM.