Drilling Technology for Deep and HPHT Containing Sour Gas well in the ChuanDongBei Field of China

ChuanDongBei Field of Sichuan Basin is a HPHT deep gas reservoir with multiple pressure systems, with maximum formation temperature up to 156 oC and pressure gradient of 1.86 at the depth of 6500m. Part of the well section contains more than 5% CO2 and near to 10% H2S, so drilling operation is extremely challenged. Firstly, this paper introduces drilling challenges such as lost circulation, severe caving-in, pipe sticking in upper section, sour gas corrosion problems, low penetration rate in the middle and deep section. Secondly, a lot of available key drilling technologies are innovated and provided, including casing program optimization, air and nitrogen drilling to improve ROP, combination drilling with anti-HT motor and fit for purpose PDC bits, anti-HT mud along with losses prevention technologies such as MPD, anti-gas channeling and big temperature difference cementing slurry in the long interval, BOP and H2S sour gas monitoring system with emergency plan and some management advices for deep HTHP containing sour gas wells. Finally, some unexpectable application results regarding these techniques to solve a series of drilling difficulties have been mentioned according to 40 wells cases. Take well LG01-XY as an example, which was improved average ROP to 6.4m/h, extended the footage to 1713m in one specialized bit with air hammer, reduced drilling period to 145days, reached “zero pollution, zero harm, zero accident†achievement during H2S interval, got premium cementing result and well bore qualify. So it could be used as a technical reference while drilling in deep HTHP containing sour gas wells in similar geologically complicated gas fields