Cementing Tight Reservoir with Low Temperature High Strength Tough Cement Slurry

The Yanchang tight reservoir in the Changqing has shallow burial depth and low static bottom hole temperature. Conventional cement slurries used in this area produced highly brittle set cements with strengths that are developed very slowly. In large-scale stimulated reservoir volume fracturing, the brittle set cement easily lost its integrity, severely endangering the production of tight oil and the production life of the well. To solve these problems, a low temperature high strength tough cement slurry has been formulated with a low temperature accelerating early strength DRA, a low temperature strengthening material DRB, a low temperature toughness improving agent DRE-300S, and some other cement slurry additives. This cement slurry, at 55℃, had 24-hour compressive strength of 35.8 MPa, and 168-hour compressive strength of 50.6 MPa. Compared with conventional cement slurries, the compressive strength of this cement slurry was increased by 33.1%, and the elastic modulus reduced by 14.3%, showing good low temperature toughness. The sealing integrity of the cement sheath under the action of alternating stresses was greatly improved. This cement slurry has been successfully used four times in cementing the φ139.7 mm production casing string in horizontal wells in Changqing Oilfield, providing a technological base for the application of low temperature high toughness cement slurries.