Research on Gas Drilling Technology

1. Overview of Gas Drilling

Gas Drilling Is Especially Suitable for the Following Situations

• hard rock
• Well wall stability is strong;
• Less formation fluid invasion;
• Formation with low to medium pore pressure;
• Water-scarce and dry areas;
• Formation sensitive to water-based or oil-based drilling fluids.

Limitations of Gas Drilling

• The intrusion control of formation fluid is not strong;
• The scope of application of the drill bit is narrow. Because the cooling effect of air on the drill bit is not strong, diamond drill bits with low high temperature resistance are seldom used in air drilling, so roller cone bits are mostly used in air drilling;
• Soft formations are not suitable for air and gas drilling. Generally, the cuttings produced in soft formations are large in size, which is not conducive to gas carrying cuttings at large well depths;
• The bottom of the well is on fire. When the bottom hole hydrocarbon gas is mixed with air to a certain ratio, combustion may occur. The branch horizontal well is used, that is, the auxiliary wells are drilled from the main wellbore in all directions to the production layer to a depth of more than 100 meters. These auxiliary wellbores are used as oil drainage channels to connect the large oil reservoirs that have not been put into development between ordinary wells.

2. Gas Drilling Technology

Wellhead Surface Control for Gas Drilling

• Meet the design wellhead pressure;
• Estimated reservoir fluid flow;
• It has been proven to be used in oil fields, safe and reliable.

Installation of Gas Drilling Equipment

The installation of air drilling equipment mainly includes: the connection between equipment, including the connection of flow meter, pressure relief valve and bypass valve, etc.; the main supply pipeline from the equipment to the drilling rig; the drilling floor manifold includes the bypass pipeline and the discharge pipeline.

Oil supply system: mist pump – so that it can start working in the shortest time when needed.

Installation of Rotary Control Head

The rotary control head should be as close as possible to the turntable, and must be centered in line with the turntable. With top drives, the centering of the rotary control head is also critical. Make sure that the kelly and drill pipe surfaces are in good condition and free from pinch marks, as this will shorten the life of the insert.

Installation of Discharge Pipeline

• Install the discharge line as straight as possible. Due to the impact of rock debris returning from the annulus at high speed, the bends of the pipeline will be quickly damaged by erosion.
• Simultaneously install kelly pressure relief pipeline, rock sample capture device and discharge pipeline ignition device.

Gas Lift

• Before gas lift, pressure tests the casing and wellhead according to the design requirements;
• Drill through the casing guide shoe, fully circulate, and clean the bottom of the well;
• Replace the drilling fluid in the well with clean water before gas lift;
• Gas lift drilling tools shall not carry downhole power drilling tools;
• Before gas lift, calculate the running depth of the drilling tool according to the well depth and the rated pressure of the supercharger;
• Before gas lift, close the sluice width from the standpipe to the pump room, the semi-sealed ram BOP and the gate valve on the discharge pipeline to the combustion pool, open the hydraulic flat valve at the front end of the throttle manifold and the valve to the sewage The gate valve on the pipeline of the pool and the outlet pipeline should be fixed firmly;
• After downhole gas lift is completed, increase the gas injection rate and fully circulate until there is no liquid drop at the outlet.

Drilling

• Before drilling, connect a lower cock and a normally closed cobalt tool check valve on the drill pipe and enter the well with the drilling tool (the cock is down);
• When drilling, the gate valves in the middle of the drilling choke manifold are in the open state: the hydraulic flat valve in front of the drilling choke manifold is in the closed state;
• Test drilling should be carried out in the early stage of drilling to adjust the reasonable matching of drilling parameters;
• Brake lever operators are required to concentrate and send the drill evenly; pay close attention to the changes in the injection pressure, gas injection volume, drilling time, turntable torque, gas detection hydrocarbon value, cuttings, and returned dust during drilling, and find abnormalities Timely report and timely processing;
• The pressurized gas supply button and the drill floor operators clearly and uniformly supply and stop the gas signal;
• When drilling directional wells, the inclination measurement frequency of the easily deviated well section should be increased; when the inclination is lower than 65°, the inclinometer should be lowered to the bottom of the well for inclination measurement with a winch; Pull out the drill, put the inclinometer into the inclinometer seat, and then use the drilling tool to send it to the bottom of the well, and start the inclinometer for a short time;

• After drilling into the gas layer, stop the gas injection, and lift the drilling tool to the safe well section.

3. Matters Needing Attention to Gas Drilling Construction

Drilling Fluid Replacement and Wellbore Drying

The preparation work for gas drilling is to hollow out the wellbore and dry the wellbore. First, determine the lifting height according to the highest gas injection pressure and drilling fluid density that the gas injection equipment can provide; use the well control device to control the pressure during the gas lift process to ensure the safety of personnel and equipment, and thoroughly dry the well wall after replacement.

The purpose of drying the well wall is not only to ensure smooth circulation without the formation of new filter cakes, but also to ensure the stability of the well wall.

Drilling

The main goal of the drilling stage is to increase the ROP and drilling time as much as possible under the condition of controlling the well deviation. There is no holding effect, and the ROP is obviously improved. With the increase of the WOB, the drilling time is obviously reduced; however, the effect is not obvious when the WOB increases to a certain value. Gas drilling generally adopts a tower drilling tool structure, which does not have the ability to correct and prevent deflection.

Therefore, in order to achieve the purpose of improving drilling efficiency, firstly, it is necessary to optimize the drilling parameters and drilling tool structure to ensure a high ROP; drilling to reduce the occurrence of well deviation, and at the same time strengthen the wellbore trajectory monitoring to ensure the wellbore trajectory control requirements.

Handling of Abnormal Situations

Formation Water

If everything is normal, you can continue drilling. If the water production is large, the torque and gas injection pressure will increase rapidly, and improper handling may cause downhole complex accidents such as pipe sticking.

Drill Sticking Phenomenon

• A large amount of water is produced in the formation, and the water and rock cuttings are mixed to form mud and filter cake, and the mud packs the drilling tool, blocking the air flow channel;
• Concurrent explosions lead to partial well wall collapse;
• Drilling encounters an unstable well section, and the well wall collapses. Therefore, attention should be paid to these matters during drilling to reduce the occurrence of accidents.

4. Conclusion