SPE-183798-MS Ultra Deepwater Cementing Development and Field Applications in Western South China Sea Hexing Liu, Zhong Li, Yi Huang, Manzong Fang, and Zhiqin Liu, CNOOC China Limited-Zhanjiang Copyright 2017, Society of Petroleum Engineers This paper was prepared for presentation at the SPE Middle East Oil & Gas Show and Conference held in Manama, Kingdom of Bahrain, 6-9 March 2017. This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright. Abstract Cementing operation of ultra deepwater well in western South China Sea is notoriously difficult due to low temperature, soft seabed and shallow water flow. Novel ultra deepwater early-enhanced strength additive PC-DA92S and PC-DA93L developed with monomer complex technology and filtrate reducer PC-DG72S developed with suspension polymerization technology have been introduced in order to cope with aforementioned problems. According to the actual conditions in western South China Sea, two sets of suitable cement slurry system have been developed. Properties of cement slurry systems have been analyzed and evaluated. After being applied in Well LSX-1-1 in western South China Sea, it is concluded that these two sets of cement slurry system are characterized by early-enhanced strength, low filtrate, outstanding anti-channeling capability, user-friendly in adjusting thickening time, and stable cement slurry rheological properties at low temperature. Therefore, the outcomes reveal these two sets of low density with early-enhanced strength Class-G Portland cement slurry system can successfully meet the requirements of cementing operation for ultra deepwater region in western South China Sea. Introduction Offshore hydrocarbon resources are mainly distributed in continental shelf, accounting for 60% of the global hydrocarbon resources. However, 30% of offshore hydrocarbon resources are distributed in ultra deepwater region. Low temperature, soft seabed and the existence of shallow water flow are the common features for such rock strata. Nowadays, ultra deepwater cement slurry system is mainly based on conventional additives and Portland cement. The early-enhanced strength and anti-channeling capabilities of cement slurry are optimized by adding low-temperature and gel strength accelerator. According to field experience that hydration and hardening capabilities of conventional cement slurry are poor under low temperature. Hence, cementing operation under ultra deepwater is not only to solve the problem of long thickening time, but also to coordinate the problem of thickening time and early-enhanced strength of set cement. Thus the demand for development of novel low-temperature with early-enhanced strength cement slurry is compelling. In order to improve the cementing quality of ultra deepwater well, the research and application of ultra deepwater cementing additives were then carried out. 2 SPE-183798-MS Development of ultra deepwater low temperature cement additive Ultra deepwater low temperature early-enhanced strength additive Conventional Class-G Portland cement has merely no hydration below 5°C within 24hrs. Moreover, the effect of conventional early-enhanced strength additive under this temperature could not reach the expectation. What makes the matter worse is the majority of additives have chloride ion, which is extremely corrosive for the casing. Therefore, additives PC-DA92S and PC-DA93L were developed by compounding 6 types of monomers. These two early-enhanced strength additives are chloride-free mixture of inorganic and organic matter. It has no corrosion to the casing and has significantly high early-enhanced strength effect under 3 ~ 30°C, which is suitable for ultra deepwater cementing operation. PC-DA92S is light gray powder with density of 2.0 g/cm3 and pH of 7-8. PC-DA93L is colorless and transparent liquid with density of 1.06-1.16 g/cm3 and pH of 7-8. When Class-G Portland cement slurry with water-cement ratio of 0.44 is added with 1% of PC-DA92S and PC-DA93L, the compressive strength of set cement is 5.5 MPa at 15 °C / 12hrs, which is 400% higher than the original slurry under same condition. The compressive strength of set cement is 4.1 MPa at 4 °C / 24hrs, which is 1540% higher than the original Class-G Portland cement slurry under same condition (as shown in Table 1). It is observed that PC-DA92S and PC-DA93L have excellent early-enhanced strength effect on Class-G Portland cement. PC-DA93L can typically shorten thickening time and PC-DA92S has better early-enhanced strength development performance. Table 1—Compressive strength under different temperature of PC-DA92S & PC-DA93L Temperature /°C Formula 1/ MPa Formula 2/ MPa 12hrs 24hrs 12hrs 24hrs 4 - 0.25 1.2 4.1 8 - 0.80 1.6 6.7 15 1.10 3.10 5.5 13.0 20 0.52 5.14 10.0 16.0 Note: Formula 1 - Class-G Portland cement + Seawater; Formula 2 - Class-G Portland cement + 1% PC-DA92S (early-enhanced strength additive) + 1% PCDA93L (early-enhanced strength additive) + Seawater. Ultra deepwater low temperature filtrate reducer Most of the filtrate reducers are polymer, which have retarding effect, such as CMC, HEC, AMPS and so on. However, under the ultra deepwater cementing conditions (below 10 °C), the retarding effect will reduce the compressive strength of set cement greatly, even without strength development in 24hrs. PCDG72S developed by polymerization technique under temperature of 10 ~ 60 °C for 2 ~ 10hrs, was a milky white solid powder with density of 1.28±0.02 g/cm3 and pH of 7 ~ 8. This additive can control filtrate of cement slurry below 40 mL under low temperature. The mechanism of this filtrate reducer is to improve the liquid viscosity of cement slurry and form thin film, thus reducing the permeability of mud cake and without affecting the development of strength of set cement. Therefore the novel filtrate reducer is suitable for ultra deepwater cementing. As shown in Table 2 and Table 3, it is concluded that 0.3% PC-DG72S can meet the requirement of filtrate control below 30°C. As the increase of dosage, the filtrate decreases, but the rheology of slurry is getting poor. Therefore, the dosage of PC-DG72S is less than 0.3%, which can meet the requirement of filtrate control for ultra deepwater cementing operation. SPE-183798-MS 3 Table 2—Filtrate control performance under different temperature of PC-DG72S Experiment condition Filtrate /mL 4°C/6.9MPa 16 8°C/6.9MPa 16 15°C/6.9MPa 20 20°C/6.9MPa 24 30°C/6.9MPa 32 Note: The formula of cement slurry - Class-G Portland cement + 0.3% PC-DG72S (filtrate reducer) + 0.2% PC-F40L (dispersant) + 0.2% PC-H21L (retarder) + Seawater. Table 3—Filtrate control performance under different dosage of PC-DG72S Dosage of PC-DG72S, % Filtrate under 15°C/6.9MPa /mL 0 >1000 0.3 36 0.5 28 0.75 20 Note: The formula of cement slurry - Class-G Portland cement + PC-DG72S (filtrate reducer) + 0.2% PC-F40L (dispersant) + 0.2% PC-H21L (retarder) + Seawater. It can be seen from Table 4 that the dosage of PC-DG72S has no effect on development of cement slurry strength at 10 °C. And it can be used to control water loss of cement slurry under low temperature in ultra deepwater well. Table 4—Affection towards the compressive strength of set cement in different dosage of PC-DG72S Dosage of PC-DG72S % Compressive strength under 10°C/21MPa / MPa 12hrs 24hrs 0 1.7 7.0 0.30 1.9 6.9 0.50 1.9 7.1 0.75 1.6 6.7 Note: The formula of cement slurry - Class-G Portland cement + 1% PC-DA92S (early-enhanced strength additive) + 1% PC-DA93L (early-enhanced strength additive) + PC-DG72S (filtrate reducer) + Seawater. Performance evaluation of ultra deepwater low temperature cement slurry Cement slurry design Ultra deepwater cement slurry systems are mostly based on Class-A, Class-G and Class-H cement, and the compressive strength of set cement is enhanced by adding early-enhanced strength additive. However, both API cement and ultrafine cement belongs to Portland cement, indicating that the hydration rate is low under low temperature. When the temperature is below 5 °C, the tribasic calcium silicate and dicalcium silicate is basically not hydrated within 12hrs. It is indispensable to add low temperature early-enhanced strength additive to adjust the overall performance of cement slurry. According to the condition of Well LSX-1-1, combined with the development of novel low temperature early-enhanced strength additive and filtrate reducer, ultra deepwater cement slurry system PC-LoSC and PC-LoIC are developed. The main formula of cement slurry is Class-G Portland cement + PC-P60 (hollow microsphere) + PC-DA92S (early- 4 SPE-183798-MS enhanced strength additive) + PC-DA93L (early-enhanced strength additive) + PC-DG72S (filtrate reducer) + PC-X61L (defoamer) + PC-F41L (dispersant) + PC-GS12L (anti-channeling additive) + Seawater. PC-LoSC slurry and performance evaluation Laboratory results indicate that long thickening time, slow development of compressive strength and poor rheology were observed at low temperature and high density of cement slurry might cause loss circulation at top hole section. Therefore, it is necessary to control thickening time, rheology and low temperature strength of set cement. The formula of cement slurry is 100.00%Class-G Portland cement + 2.00%PC-DA92S (early-enhanced strength additive) + 1.00%PC-DA93L (early-enhanced strength additive) + 0.10%PCX61L (defoamer) + 45.25% Seawater + 19.00%PC-P60 (hollow microsphere). The properties of cement slurry are listed in Table 5. Table 5—Properties of PC-LoSC system Strength/MPa Rheology Density/ g / cm Thickening time/ hr: min 12hrs 24hrs φ300 / φ200 / φ100 / φ6 / φ3 1.40 3:58 3.7 13.8 138/114/90/29/22 3 The slurry sample was cured under 10°C. The compressive strength of set cement reached 3.7 MPa in 12hrs, which meets the requirement of surface casing cementing. PC-LoIC cement slurry and performance evaluation According to the conditions of Well LSX-1-1, the formula was optimized by using novel ultra deepwater low temperature filtrate reducer additive. The cement slurry formula for 13-3/8" casing cementing operation was determined, and the slurry rheological properties were evaluated. The formula of lead slurry is 100.00%Class-G Portland cement + 71.29%Seawater + 19.00%PC-P60 (hollow microsphere) + 0.80%PC-DA92S (early-enhanced strength additive) + 0.80%PC-DA93L (earlyenhanced strength additive) + 0.30%PC-DG72S (filtrate reducer) + 3.50%PC-F41L (dispersant). The lead slurry sample was cured under 18°C and the properties of lead cement slurry are listed in Table 6. Table 6—Properties of lead slurry of PC-LoIC system Density/ g / cm3 1.40 Strength/MPa Rheology Filtrate/mL Thickening time/ hr: min 12hrs 24hrs φ300 / φ200 / φ100 / φ6 / φ3 18 5:45 3.7 13.8 138/113/86/34/30 The formula of tail slurry is 100.00% Class-G Portland cement + 70.54%Seawater + 19.00%PCP60(hollow microsphere) + 4.00%PC-GS12L(anti-channeling additive) + 0.80%PC-DA92S (earlyenhanced strength additive) + 0.80%PC-DA93L (early-enhanced strength additive) + 0.30%PC-DG72S (filtrate reducer) + 2.50%PC-F41L(dispersant) + 0.40%PC-X66L(defoamer). The tail slurry sample was cured under 20°C and the properties of lead cement slurry are listed in Table 7. Table 7—Properties of tail slurry of PC-LoIC system Strength/MPa Rheology Density/ g / cm3 Filtrate/mL Thickening time/ hr: min 12hrs 24hrs φ300 / φ200 / φ100 / φ6 / φ3 1.90 18 4:30 3.0 8.1 151/127/103/35/30 SPE-183798-MS 5 It can be seen that the overall performance of lead and tail slurry is exceptional under laboratory evaluation test. The variation of thickening time is negligible when the environment conditions are slightly adjusted, and there exhibits no risks to cementing operation. Moreover, the compressive strength after 12hrs of lead and tail slurry has achieved design requirement, with acceptable filtrate and excellent rheological properties. Field applications The well LSX-1-1 is of three layers of casing with water depth of 1720m. The first spud of 36" hole with 36" conductor jetted in place and 26" hole was drilled to the depth of 2194m RKB with 20" surface casing set at 2188m. The bottom hole static tempertature (BHST) of tophole cementing was 29 °C, and the bottom hole circulating tempertature (BHCT) was 13 °C. The second spud of 17-1/2" hole was drilled to 2617m RKB, and 13-3/8" casing was set at 2610m RKB. The BHST of intermediate casing cementing was 34°C and the BHCT was 20°C. The third spud of 12-1/4" hole reached TD at 2912m RKB without running 9-5/8" casing. The cement plug of 20" surface casing was drilled out after 120hrs with BOP stacks landing on high pressure wellhead (HPWH). The cement plug was tagged at 2159.2m, which is identical with cementing design. The parameters of drilling out cement plug are as follows : weight on bit (WOB) 2 ~ 15 klbs, rotational speed (RPM) 60, pump displacement 4320 L / min, stand pipe pressure(SPP) 13.1 ~ 13.8 MPa, torque(TRQ) 1 ~ 15 klb*ft. As shown in Fig.1, the shape of cement return from shale shaker was regular with cutting trace can be identified clearly, indicating set cement had developed high strength. Figure 1—Cement return from shale shaker The cement plug of 13-3/8" intermediate casing was drilled out after 31hrs. The dart was tagged at 2578.7m, which is identical with cementing design. The parameters of drilling out cement plug are as follows: WOB 2 ~ 10 klbs, RPM 50~80, Pump displacement 3000~3550 L / min, SPP 8.3 ~ 10.7 MPa, (TRQ) 1 ~ 10 klb*ft. As shown in Fig.2, the annuli between 13-3/8" casing and wellbore had been effectively isolated and the strength of set cement had also fine developed. Figure 2—SBT of 13–3/8" intermediate casing Hence, the novel additives played a significant role in ultra deepwater cementing operation. The performance of cement slurry achieved requirements, solving cementing problems of ultra deepwater surface and intermediate casing under low temperature. 6 SPE-183798-MS Conclusions 1. The additives PC-DA92S and PC-DA93L have outstanding early-enhanced strength performance under low temperature and have no adverse effect to the cement slurry and casing. 2. The additive PC-DG72S with dosage of 0.3% could meet the requirement of filtrate control for cement slurry under low temperature and has no adverse effect on the development of strength. 3. This novel cementing technology can provide future direction for the field applications of ultra deepwater cementing operation and guidance for the technology development. Moreover, it can pave the road to the exploration of potential natural gas resources in western South China Sea. Acknowledgments This work is supported by the National Science and Technology Major Project (Project No. 2016ZX05028001-009). References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. Ye Zhi, Fan Honghai, Zhang Guobinet al, Investigation of shallow water flow in deepwater drilling[J]. Petroleum Drilling Techniques, 2010, 38(6):48–52. Wang Qingshun, Zhang Qun, Xu Shaochenget al, Temperature prediction technique for deepwater cementing operations[J]. Petroleum Drilling Techniques, 2006, 34(4):67–69. Ravi K, Biezen E N, Lightford S Cet al, Deepwater cementing challenges[R]. SPE 56534, 1999. Armstrong L J, Jean P, Puz G. Deepwater development environmental issues and challenges[R]. SPE 73873, 2002. Rae P, Gino Di Lullo. Lightweight cement formulations for deepwater cementing:fact and fiction[R]. SPE 91002, 2004. Boncan G. Methods and compositions for use in cementing in cold environments:US, 6626243LPJ. 2003-09-30. Watson P, Kolstad E, Borstmayer Ret al, An innovative approach to development drilling in deepwater gulf of Mexico [R]. SPE／IADC 79809, 2003. Jenkins R W, Schmidt DA, Stokes Det al, Drilling the first ultra deepwater well offshore Malaysia[R]. SPE／IADC 79807, 2003. Luiz A S R, Jurlqueira P, Roque J L Overcoming deep and ultra deepwater drilling challenges[R]. OTC 15233, 2003. Bannerman M, Calvert J, Griffin T. New API practices for isolating potential flow zones during drilling and cementing operations[R]. SPE 97168, 2005. Baireddy R R, Ronald J C, Bryan K W. Early-enhanced strength cement compositions and methods: US, 6478868[P]. Xu Mingbiao, Zeng Jing, Tang Haixionget al, Research on cement slurry for deepwater cementing operation in zero thickening transition period at low temperature[J]. Journal of Oil and Gas Technology, 2007, 29(3):104–107. Wang Xiaoliang, Xu Mingbiao, Wang Qingshunet al, Research on Class-G—Portland cementing slurry in surface casing in deepwater[J]. Petroleum Drilling Techniques, 2010, 38(6):11–14.