Development of heat-resistant ultra-fine cement for well cementing to improve oil and gas recovery efficiency
Abstract
In the oil and gas industry, squeeze cementing is a widely adopted technique to repair cement sheath defects, particularly to eliminate the pressure differentials between the casing annulus and the flow outside the casing. The ability of mortar to penetrate fracture networks and micro-sized pores depends significantly on the particle size distribution of the binder used. Replacing conventional well cement with ultra-fine ground cement for squeeze applications is an effective solution to improve the quality of the cementing process. This study focuses on developing a heat-resistant ultra-fine cement (d50 ≤ 6 μm), stable up to 160°C and non-shrinkage within the temperature range of 50 - 160°C, from primary feedstocks such as Portland cement clinker, phosphate slag, and silica sand. The raw materials were mixed to ensure thermal stability and shrink-resistance criteria, aiming to identify the most feasible optimal formulation for producing this ultra-fine slag - Portland - silica cement.
The evaluation of the cement powder indicates that the selected components meet the particle-size requirements (d50 ≤ 6 μm; d95 ≤ 16 μm). The assessment of the mortar and hardened cement derived from the ultra-fine slag – Portland - silica cement exhibited volumetric expansion at both low (< 76°C) and high (> 76°C to 160°C) temperatures, with expansion levels meeting sulfate durability and shrink resistance standards. This confirms that the cement is entirely shrinkage-free within the temperature range of up to 160°C. Additionally, the compressive strength achieved was 1231 - 1413 psi under conditions of 120 - 160°C and a pressure of 210 atm, well above the ≥ 500 psi threshold specified for oil well squeeze cementing. The research team successfully identified an optimal blend design and validated the practical feasibility of producing a heat-resistant ultra-fine slag - Portland - silica cement for squeeze cementing applications.
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