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The Austin Chalk is an upper Cretaceous geologic formation in the Gulf Coast region of the United States. For the purpose of this paper, this Austin chalk under consideration is in central Texas. The formation is known for having a wide range in pressure differential, making it difficult to predict the fracture and pore pressure limits on some of the wells. Due to this uncertainty, some operators tend to assume the well problems are related to ballooning/breathing. This assumption leads to drilling issues such as but not limited to stuck pipe, excessive mud losses, and tripping challenges.
With reference to this SPE paper, An operator had encountered some of the mentioned issues above in their previous wells and was looking for a CBHP MPD solution, capable of bridging their internal knowledge gap to becoming MPD aware. MPD was rigged up prior to drilling the horizontal production hole at ±13,000 ft MD. The initial mud weight was 10.5 ppg with MPD maintaining an 11.4 ppge. Later a high-pressure zone was encountered at ±13,500 ft MD requiring 11.6 ppge to control the formation fluid. Drilling continued until ±16,000 ft MD where an 11.5 ppge loss zone was encountered. Therefore this well had no drilling window.
The window stabilized after circulating a few bottoms up with backpressure and lost circulation material. MPD minimized mud losses/gains and helped reach TD safely. At TD, a bigger challenge was how to trip out without swabbing. The Tripping was achieved by placing a heavy pill above the high-pressure gas zone and avoiding the loss zone. When tripping pipe and casing, proper fill was achieved by circulating kill weight mud across the well with MPD. The casing and cementing operation was subsequently conducted and was successfully completed with the utilization of MPD.