A Low-Cost and Low-Density Cement Slurry System Suitable for a Shallow Unconsolidated Stratum

Jiaping Yue,Yanan Geng,Jie Wang,Zhaonian Liu,Ting Sun,Zhiqiang Wu

doi:10.1155/2020/1628281

Abstract

The shallow unconsolidated stratum in the offshore oilfield is characterized by large porosity, low temperature, and weak formation and often faces problems such as low density and poor compressive strength of a cement slurry, among others, which pose serious challenges to construction. A high-performance low-density cement slurry system must be used for cementing to ensure the safety of subsequent drilling and mining on-site and to reduce the cost of cement slurry for the efficient development of oil and gas fields. Based on these problems, according to the principle of particle gradation, a mixture with a high accumulation rate and low density composed of five types of mineral materials, i.e., artificial microbeads, floating beads, microsilicon, fly ash, and slag, has been developed through a large number of indoor experiments, and a set of low-cost and low-density cement slurry systems has been developed; these systems are suitable for the shallow loose formations of offshore oil fields. The cement slurry system meets the requirements of the cementing operation conducted under different temperatures and pressures. The density range is 1.4–1.7 g/cm3, which can be adjusted. The cement slurry is stable and exhibits good fluidity. The thickening time meets the requirements of cementing construction. Moreover, the compressive strength of the cement paste is high, and the compressive strength of cement paste is greater than 12 MPa for 24 h and 14 MPa for 48 h of curing at 50°C, which maximizes the economic benefits. The research results provide technical support for the safe and efficient development of offshore oil and gas fields.

Highlights

Based on these problems, according to the principle of particle gradation, a mixture with a high accumulation rate and low density composed of five types of mineral materials, i.e., artificial microbeads, floating beads, microsilicon, fly ash, and slag, has been developed through a large number of indoor experiments, and a set of low-cost and low-density cement slurry systems has been developed; these systems are suitable for the shallow loose formations of offshore oil fields. e cement slurry system meets the requirements of the cementing operation conducted under different temperatures and pressures. e density range is 1.4–1.7 g/cm3, which can be adjusted. e cement slurry is stable and exhibits good fluidity. e thickening time meets the requirements of cementing construction
Introduction e cement slurry system has a low compressive strength, slow development, and poor cementation quality at the second interface and other problems caused by the high porosity, poor cementation degree, and low temperature of the unconsolidated sandstone stratum in the offshore oilfield [1]
Microsilicon with a small particle size is a good plugging agent that effectively fills the voids in the cement particles and increases the packing volume fraction (PVF) value of the cement slurry; in addition, the microsilicon hydration reaction produces a C-S-H gel and increases the strength of the cement stone

Summary

Materials and Methods

E function of the retarder is to adjust the thickening time of the cement slurry, the dispersant improves the fluidity of the cement slurry, and the defoamer is used to reduce the number of bubbles in the cement slurry. E early strength agent improves the early strength of the cement slurry, and a filtration reducer is mainly used to decrease the water lost from the cement slurry. E microbead is an artificially fabricated silicate glass sphere with a high compressive strength that is not broken [13]. It has several damage grades, the most common of which are 2000 psi, 4000 psi, 6000 psi, and 10,000 psi.

Experimental Methods

Results and Discussion

Conclusions