Research on Cementing Technology in Narrow Gaps at Changqing Gas Field

As a typical “three-lows” characteristic of low permeability, low pressure, and low abundance, the Changqing gas field has been developed from straight and directional wells to horizontal wells. And the poor effectiveness of the lateral sealing is due to the application of casing without cementing completions or bare borehole completions. To ensure the quality of cementing with a small annular space gap, a mechanical coupling model of “casing-cement sheath-formation” was established, and mechanical simulations were conducted for both pressurized and unpressurized conditions under alternating stress to determine the performance of the required cement slurry. Then toughened materials were optimized to develop a high-toughness cement slurry and high-performance front liquid system with high flexibility and impact resistance. Subsequently, simulations were conducted in small borehole wells to improve replacement efficiency and optimize construction displacements. A series of process technologies for cementing long horizontal sections under narrow gap conditions was formed by optimizing conducting replacement efficiency simulations and construction displacements in small boreholes. It has been fully promoted and applied to achieve the renewal of the well-completion method. The initial daily gas production was increased by 25% compared with the bare-hole completion wells through the late production evaluation of the block. It has achieved the purpose of improving single well production and wellbore integrity, which is an important reference for unconventional small borehole cementing and effectively contributes to the development of the Changqing gas field.