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.

The overall liner cementing qualification rate is only 40% in Agadem block of Niger, The cement slurry system used in the field has a UCA transition time of 43min, and an expansion rate of -0.03% in 24h, which result in a poor anti-gas channeling performance. The expansive agent and the anti-gas channeling toughening agent of anti-channeling agent were optimized through experiment study. A novel micro-expansion anti-gas channel cement slurry system which is suitable for Agadem block was obtained through experiment optimization study: 100% G +2 ∼ 4% fluid loss agent +3 ∼ 4.5% anti-channeling agent +1 ∼ 2% expansion agent-100S +0.15 ∼ 0.4% retarder +0 ∼ 0.3% dispersant +0 ∼ 0.25% defoamer + water. This new cement system has a good anti-gas channeling performance, the cement strength is 24.5-35.0MPa after 24hrs, the UCA transition time is 16-18min, and the expansion rate is 1.5-1.7%. At the same time, a cementing prepad fluid suitable for the block and the micro-expansion cement slurry system is selected to ensure the performance of the cement slurry's anti-channeling performance. The field test results proofs the good performance of the new cement system. The cementing qualification rate of Koulele W-5 well is 96%, and the second interface cementation is Good. The cementing qualification rate of Trakes CN-1 well is 100% which second interface cementation is Excellent. This paper has positive guidance and reference for cementing in Agadem block.

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