The First Of Its Kind in China! Fuling Shale Gas Field Drilling “Three Downsizing” Technology Improves Oil And Gas Development Benefits

Recently, the first slimmed-down III well in the Fuling shale gas field, the Jiaoye 23-Z2HF well, was successfully completed. The well adopted the country's first slimmed-down III well structure technology, which significantly reduced the investment cost of the drilling project and met the needs of shale oil and gas. Reservoir stimulation requires releasing a large number of well locations, which is of great significance to accelerating the efficient and low-cost development of domestic shale gas.

Fuling Shale Gas Field Drilling "Three Downsizing" Technology Improves Oil and Gas Development Benefits

Benefit development urgently requires technological evolution
In the early stages of Fuling shale gas field exploitation, the drilling well structure was a wellbore with a diameter of 215.9 mm and a casing with a diameter of 139.7 mm. Due to the large size of the well body, the drilling cycle was long, the material input was high, and the drilling cost was high. At that time, the Baima, The low output of deep-seated blocks such as Fenglai also results in a low input-to-output ratio, making it impossible to achieve profitable development.
In order to reduce costs, from 2020 to the end of 2022, Jianghan Oilfield proposed and successfully developed two types of wellbore structures: slimming type I and type II. Among them, slimming type I is the first domestic technology, and type II is the first international technology. The slimmed-down type I well structure uses a 171.5 mm diameter wellbore, matched with a 114.3 mm diameter casing completion, and is used for shallow wells with a vertical depth of less than 3,500 meters. The slimmed-down type II well structure uses a 190.5 mm diameter wellbore, matched with a diameter of 139.7 mm casing completion is used for deep wells with a vertical depth of more than 3,500 meters.
"Compared with the traditional conventional well structure, the slimmed-down well structure reduces the size of each wellbore and the size of the casing respectively. After being promoted and used in the Fuling shale gas field, it has reduced the amount of materials such as casing and solid waste from the source. production, reduce drilling costs, and have a very good effect of reducing costs and improving efficiency." said Lu Heping, vice president of the Academy of Engineering.
As gas field exploration and development moves to the Fuxing block, the abundance of oil and gas reserves in the Fuxing continental shale is relatively low. To achieve profitable development, a larger scale of reconstruction is required to provide single well reserves, and the casing is required to be appropriately increased to meet the needs of larger fracturing construction displacement. If a slimmed-down I wellbore structure is adopted, the smaller wellbore will meet the slimming requirements, but the casing will be smaller and will not meet the reservoir stimulation requirements. If a slimmed-down II well structure is adopted, its larger casing size will meet the needs of reservoir stimulation, but the project cost will increase, making it difficult to achieve profitable development.
Faced with the problem of efficient development, oilfield technicians and experts decided to develop a new well structure that meets the development conditions of new blocks such as Fuxing.

Fuling Shale Gas Field Drilling "Three Downsizing" Technology Improves Oil and Gas Development Benefits

"Insert the thin wire into the small eyeworm hole in the tree trunk"
Oilfield drilling experts decided to further slim down the slimming type I well structure, keeping the completion hole size unchanged at 171.5 mm, changing the outer diameter of the completion casing size from 114.3 mm to 127 mm, and successfully developed the slimming type III well structure. technology.
Qin Wenbin, an expert in oilfield drilling technology, said that this new well structure is the first of its kind in China and has two unprecedented problems that need to be overcome.
First, with the Slim Type III wellbore structure technology, a 127 mm diameter casing must be run through a 171.5 mm diameter wellbore to the bottom of a 171.5 mm diameter long horizontal section, but the gap between the wellbore and the casing is only 22.5 mm, and The wellbore is more than 5,000 meters long and is divided into vertical well sections, inclined well sections and horizontal well sections. The wellbore trajectory is very complex and it is extremely difficult to run it in.
"The descent process is like inserting a thin wire into a small wormhole on a tree trunk. The wormhole is small, long, and winding. The thin wire goes smoothly when it first enters the wormhole, but as the thin wire deepens, Either the thread tip is on the side wall of the wormhole, or the thread bends with a little force, and the thread tip is difficult to insert to the end. Therefore, to solve this problem, we must start from the well trajectory, drilling fluid lubrication, operating measures and pipe string structure. Carry out technical research to ensure that the wellbore trajectory is smoother and more regular.
Second, the Slim III wellbore structure technology is adopted. When the casing is placed in the wellbore at the center, the operator will pour cement into the annular space between the casing and the wellbore wall to form an annular space cement ring. Subsequently, The staged fracturing operation will open a hole in the cement sheath as a channel to connect the wellbore and the stratum outside the wellbore, so that the fracturing fluid poured from the wellbore during the later fracturing operation can enter the stratum outside the wellbore through the channel and carry out fracturing operations. . If the position of the casing placed in the wellbore is not centered, the casing will touch the wellbore wall and form a wall in the annular space. The cement poured later will not be able to pass through the wall, forming a dead space under the wall without cement pouring. The fracturing fluid easily leaks into dead corners, causing defects. It does not have enough force to tear open the formation to release shale gas, and the shale gas will move upward along the loosely sealed cement ring to the wellhead, causing safety accidents. Therefore, it is very important to keep the casing centered, and technical research needs to be carried out to ensure cementing quality.
Once these two main research ideas have been determined, researchers from the Academy of Engineering will have a research direction.

Fuling Shale Gas Field Drilling "Three Downsizing" Technology Improves Oil and Gas Development Benefits

Systematic innovation to solve problems
In order to solve the above problems, researchers from the Academy of Engineering have carried out a large number of systematic innovative research.
For example, to solve the problem of smoothly running the casing into the wellbore, how to ensure that the wellbore is flat and smooth during construction. To this end, researchers from the Academy of Engineering designed a reasonable well trajectory after research, and through reasonable parameter control during construction, a regular and flat long horizontal wellbore was drilled.
Researchers have also developed a drilling fluid system with upgraded rheology and lubricity. When used in small-hole drilling construction, it not only ensures that the wellbore does not collapse, but also ensures that the wellbore is smooth and has less friction.
Whether the casing can be smoothly run down to the bottom of the wellbore with a small gap is also a difficult problem. After researching key problems, the researchers first added a roller centralizer and guide shoes to the bottom of the casing to keep the lowermost casing in a "head-up" state to ensure that the casing will not poke the well wall when it is lowered into the wellbore. Second, alternately install roller centralizers and rigid centralizers in the casing to center the casing in the wellbore, reducing the contact between the casing body and the well wall, minimizing friction, and making running smoother. In addition, the researchers also developed strict casing running measures to ensure that the casing can be smoothly run into the wellbore with a small gap.
The slimmed-down III well structure has small gaps, and the cementing process is the last serious challenge. Researchers have developed a suitable cement slurry formula to ensure that the cement slurry can flow smoothly and not solidify during the construction process of the small wellbore, and can also ensure the strength of the cement after solidification. Secondly, in view of the fact that the annular space gap between the casing and the wellbore is smaller, which may easily lead to excessive pressure when injecting cement slurry and crushing the formation, thereby causing the risk of cement slurry leaking into the formation. After research, researchers finally developed Cementing technology that ensures good fluidity, no leakage, high displacement efficiency, good sealing quality during cement injection, and a qualified wellbore for subsequent production.
In the end, based on the research results, the engineering designers comprehensively designed a slimming III well structure design plan, overcame a series of three well body slimming problems, and decided to start the construction test in the Jiaoye 23-Z2HF well.
The test was launched in June 2023. On October 9, 2023, the oil field's first "slimming type III well" Jiaoye 23-Z2HF well was successfully completed. The well was drilled to a depth of 5,011 meters, a horizontal section of 1,961 meters, and a drilling cycle of 33.88 days. At the same time, compared with the slimming type II well, the cost is saved by another 8%. The well test was successful, verifying the feasibility of reducing the wellbore annulus gap under the existing drilling technology conditions, realizing the iterative upgrade of the slimmed-down wellbore structure, laying a solid foundation for subsequent promotion and application, and also for the next step of realizing the Fuxing Block The goal of a 20-day drilling cycle has taken a critical step.
Industry insiders believe that the "Slim Type III" wellbore structure has been successfully researched and tested, especially the design concept of using a 171.5mm diameter wellbore to run a 127mm diameter casing, which is an international first and has opened up a new path for speeding up the source, reducing costs and increasing efficiency. New ideas help achieve long-term stable, high-yield and profitable development of shale gas. At the same time, this well structure can be promoted in various blocks of Jianghan Oilfield to achieve a new model of cost reduction and growth in oilfield development, which will make greater contributions to achieving the "Thousands and Hundreds" strategic goal of the oilfield and ensuring national energy security.