Abstract

Objective of this study is to shed light to critical well control parameters of horizontal shale gas wells drilled with oil based muds (OBM). This study utilizes an interactive well control simulator to re-evaluate the kick control procedures in water based mud (WBM) and verify its application to oil based mud. Due to gas solubility in OBM a real time drilling and hydraulics data analysis is essential to minimize kick volumes. Therefore, early kick detection and surface warning signs are critical to minimize the influx size and reduce wellbore pressures. Moreover, the impacts of water-to-oil ratio, gas solubility, kick size, influx type and circulation rates on well control are investigated. OBM kick control process in horizontal wells creates additional challenges since the surface pressure and volume are not representative of the bottom-hole conditions. In unconventional shale gas reservoirs, oil and synthetic based drilling fluids are very common. Drilling cost, log interpretation, and environmental impacts are the main drawbacks of OBM. However, wellbore stability, reduction in torque and drag, stability of mud properties at higher temperatures and better drilling performance are the main advantages of OBM. Preliminary results show that dissolved gas in oil is liberated at the bubble point pressure and complicates surface kick handling procedures. Choke adjustment is hard due to the unexpected high volume of gases released and the delay time of choke response. Early detection is a key factor in minimizing the influx size and properly controls the casing shoe and choke pressures. Based on 110 hours of real time interactive simulation, influence of gas solubility on well control in OBM is presented to improve rig and personnel safety and reduce the blowout associated risks.

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