Chongqing - On September 27, the 2024 high-quality development research tour arrived at the Sinopec Jianghan Oilfield Jiaoye 77 Platform in Chongqing Fuling to explore the "slimmed down" shale gas extraction wells.

As the country's first large-scale shale gas field to enter commercial development in 2014, Fuling has become a clean energy source for more than 70 cities along the Yangtze River Economic Belt in China, according to a Xinhua report in April. 

Huxin Luo, a Bridging News reporter, learned from the drilling site that, similar to how humans lose weight through dieting and exercise, extraction wells can achieve a "slimming" effect by using techniques to reduce drilling bit and casing sizes while maintaining clarity on the geological structure and drilling risks.

Why are they "slimming down" extraction wells? Zhang Yuqiang, Deputy Manager of the Oil and Gas Production Capacity Construction Management Center in Jianghan Oilfield, explained, "Drilling is like constructing underground passages for oil and gas, and narrowing the passage requires reducing the materials."

The drilling equipment at the Jiaoye 77 Platform is currently in operation. (Photo/Huxin Luo)

Ye Xin, the Center's deputy director, said that reducing the size of extraction wells can lower average costs by about two to three million yuan per well. According to statistics, the Center has drilled 97 slimmed wells, saving over 200 million yuan in total drilling costs.

However, reducing well size increases drilling difficulty. Ye noted that the smaller bore destabilizes downhole equipment, necessitating technological upgrades. The reduced casing size raises pressure with depth, making materials more pliable and causing drill bits to shift, complicating operations. Additionally, Gamma-ray logging signals, used to identify target layers, may be interfered with.

According to Ye, "slimming down" a well is not just a technical upgrade but a "zero-based R&D" effort, requiring upgrades to all drilling equipment and technology. Relevant personnel noted that reducing well size represents a "revolutionary" technological advancement that will drive upgrades across all related equipment.

Moreover, well size cannot be arbitrarily reduced; different types must be chosen based on specific geological conditions. Zhang noted, "Narrowing extraction wells in shale gas fields is pioneering for Jianghan Oilfield. We validated the technical solutions 30 to 40 times, meticulously modifying every detail." 

Two structural types were proposed: Type I for the target layer above 3,500 meters with smaller bore and casing sizes and Type II for the layer below 3,500 meters with slightly larger sizes.

Workers are inspecting the pumping equipment. (Photo/Fuling District)

Ye indicated that the Jiaoye 77 Platform employs Type II, with plans to drill ten wells, of which four have been completed, each with an engineering cycle of approximately 35 days. He noted that slimmed well technology leads the field in China.

The relevant personnel explained the process for extracting shale gas as follows: first, an L-shaped well is drilled, then fracturing equipment injects water into the horizontal section to compress the target layer and release natural gas. Gas collection equipment is then used to gather and transport the gas. Managing the water involved in these steps is the most challenging part of the process.

Zheng Ruibo, a gas extraction expert at Fuling Shale Gas Company, said, "Water aids in our shale gas extraction, but we must ultimately contend with it." He explained that while the initially released natural gas has enough pressure to expel water from the well, as the energy decreases over time, water begins to accumulate, significantly obstructing the flow.

Zheng highlighted that liquid accumulation in the horizontal section is a global issue. Recently, his team made a breakthrough by installing equipment inside the horizontal section for continuous water drainage, unlike traditional external pumping methods. This solution is currently being evaluated, and ongoing observation is needed to assess natural gas collection rates.