Advanced Cementing Systems for Deep Sour Gas Wells
- Z. Liu (SINOPEC) | J. Sun (SINOPEC) | H.A. Nasr-El-Din (Texas A&M University) | H. Shan (OPT Co.) | Z. Xiao (OPT Co.)
- Document ID
- Society of Petroleum Engineers
- SPE/DGS Saudi Arabia Section Technical Symposium and Exhibition, 15-18 May, Al-Khobar, Saudi Arabia
- Publication Date
- Document Type
- Conference Paper
- 2011. Society of Petroleum Engineers
- 5.1.1 Exploration, Development, Structural Geology, 1.11 Drilling Fluids and Materials, 5.2 Reservoir Fluid Dynamics, 1.14.3 Cement Formulation (Chemistry, Properties), 2.7.1 Completion Fluids, 1.14 Casing and Cementing, 5.4.2 Gas Injection Methods, 2 Well Completion, 4.2.3 Materials and Corrosion, 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 4.3.1 Hydrates
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Cementing deep sour gas wells presents a number of challenges to well construction engineers. High bottom hole static temperature (BHST from 250 to 400oF) and pressure (mud density > 2.0 g/cm3), excessively long job times due to the constraints imposed by tight annular clearances (casing OD/hole size > 0.85), long cement columns (interval length > 450 ft), and harsh conditions (H2S, CO2, salt layer, high leakoff). All of these factors contribute to the operational risks not only during placement of the cement slurry in the wellbore, but also during the life of the well. Field data indicates that current cement systems were not able to address these challenges, and as a result, the outcome obtained from various cementing jobs was below expectation.
Advanced cement systems were developed to address the problems encountered in cementing deep sour gas wells. These systems were applied in the field with great success. Multi-functional fluid migration control systems together with engineering particle sizing technique significantly improved the performance of cementing jobs, including: superior fluid migration control, predictable thickening time, stable API properties at high slurry densities, and great resistance to H2S, CO2 and salt corrosion. A unique retarder used in the lead slurry helped in developing compressive strength rapidly on the top of cement column. An effective laminar flow displacement technique was also used to displace drilling fluids effectively to enhance its placement and improve the cementing bond.
This paper details a thorough and systematic laboratory development of innovative cement systems and presents case histories to document their effectiveness for cementing deep sour gas wells.
Engineers pay more attention to the exploration and development of gas reserves due to the increasing demands of hydrocarbon resources in the last decades. However, most gas reserves in the world contain sour gases such as H2S and CO2. It is reported that more than 40% of deep sour gas reserves contain more than 2 mol% CO2 and more than 100 ppm H2S (Arnold 1980).
Cementing high temperature deep sour gas wells presents a number of challenges to well construction engineers. High bottom hole static temperature (BHST from 250 to 400oF) and pressure (mud density > 2.0 g/ml), excessively long job times due to the constraints imposed by tight annular clearances (casing OD/hole size > 0.85), long cement columns (interval length > 450 ft) all contribute to the operational risks not only during placement of the cement slurry in the wellbore, but also during the life of the well.
Sour gases such as H2S and CO2 bring additional challenges to deep gas well cementing. A few studies have been conducted to examine the effects of H2S on oil well cementing due to its high hazards and risks. Several studies however, are available that investigate the impact of CO2 on oil well cements (Newton and Hausler 1984; Onan et al. 1984). H2S has destructive effect on oil well cements becasue it reacts with metal hydroxides in cements and forms metal sulfides, which could cause collapse of set cements (Guo et al. 2004).
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