Research On Cementing Technology Of Shale Gas Horizontal Well In Changning-Weiyuan Area

Si Chuan basin is the most favorable and important area for shale gas exploration in China which possesses aboundant shale gas resource. Therefore, shale gas exploration and development pilot test and Chang Ning-Wei Yuan Demonstration Area has been established in Si Chuan basin.Shale gas reservoir with characteristics of source and reservoir in the same bed, low natural deliverabiliry, low porosity, low permeability and water sensitivity. In Chang Ning-Wei Yuan area, horizontal well volume fracturing has been adopted as major method to achieve commercial exploration and high economic benefit. To ensuring borehole stability, oil-based mud (OBM) has been used in horizontal section drilling. These technical measures have brought a series of problems and challenges for cementing engineering:the incompatibility of OBM and cement slurry may cause setting time prolonged or shorten manifold, low cementation and poor mechanical properties of cement sheath; volume fracturing may seriously damage cement sheath due to exceeding pressure and thus zonal isolation failures. Hence, one of the unneglectable factors of shale gas well construction is how to maintain the long term zonal isolation.Based on a comprehensive review on the present technology of shale gas horizontal well cementing and problems of shale gas well cementing in Chang Ning-Wei Yuan area, laboratory experiment was ran on evaluation methods, materials selection, cement performance test and process optimization. Compatibility of OBM and cement was evaluated which exhibits a bad influence on cement slurry's fluidity, settting time, compressive strength and bonding strength. Oil droplet cannot participate in cement hydration, it disperses in cement paste to form honeycomb holes. An evaluation method of surfactant effects according to rationale and characteristic of surfactant and spacer requirement was established. The key concept of this method is the relationship of surface tension and wetting ability, flushing efficiency and interface bonding strength. A surfactant SD80 with well flushing efficiency and interfacial wetting effect and a polysaccharide polymer suspending agent SD85 with higher temperature tolerance was optimized. And on this basis a spacer was developed. Compressive strength, tensile strength and triaxial mechanics testing were conducted to evaluate polyester fiber, inorganic mineral fiber, ceramic fiber and carbon fiber modified cement mechanical properties and inorganic mineral fiber SD66 was optimized as reinforcing and toughening material. SDP-1 was optimized as expansion agent by linear expansion testing at atmosphere and volume shrinkage testing at HTHP. Sand-carrying process, centralizer placement design and calculation, drilling fluid rheological adjusting, pump pressure and delivery capacity optimization were analyzed. The study results were applied to 6 shale gas well cementing operation in Chang Ning-Wei Yuan area, and have obtained well effects.