The shaft is composed of multiple concentric steel pipes and reinforced with cement. The first layer of pipeline running in the oil well is called conduit, which is used to establish the initial drilling fluid circulation channel and protect the ground near the wellhead. The second layer of pipeline that the oil well runs into is called surface casing, which is usually tens to hundreds of meters, and its function is to block the unstable soft stratum and shallow water stratum on the upper part; The third casing run in an oil well is called technical casing, which is run in order to ensure that the drilling can reach the design depth when encountering complex formations such as high pressure oil, gas, water layer, lost circulation layer and collapse layer in the middle of drilling. The innermost casing running in an oil well is called reservoir casing, and the running depth of reservoir casing depends on reservoir depth and completion structure. Its function is to seal oil, gas and water layers and establish a long-term oil and gas production channel. The casings of the above layers shall be cemented with the stratum and connected with the wellhead device to form a permanent passage. During normal oil production, the tubing should be run again, so as to carry the oil pump and various tools into the well and export oil and gas through it.
After the steel pipe was lowered into the well, only drilling was made, but the passage was not perfect and completion was needed. Completion is the communication mode between oil and gas reservoirs and the bottom hole and the operation of bottom hole structure, which is selected to meet the production needs of oil and gas reservoirs with different properties. Open hole completion method means that the whole oil layer is completely exposed without casing, and the oil layer is directly connected with the ground through the oil well. This method is often used in rural wells. Perforation completion method is one of the most widely used methods in oil well completion. It refers to a completion method which aims at the oil and gas reservoir with a special gun, shoots through the casing and cement sheath, enters the formation to a certain depth, and makes the oil and gas flow into the wellbore through perforation holes, so that the oil reservoir communicates with the wellbore. Through-hole completion method means that after drilling through the oil and gas layer, the casing with holes is lowered to the oil and gas layer, and oil and gas flow into the wellbore from the formation through the holes. The completion method of gravel screen pipe is to wind the screen pipe under the oil layer, and then fill gravel with a certain particle size between the screen pipe and the borehole wall. Oil and natural gas can flow into the wellbore through screens and gravel layers.
Once the wellbore is connected with the oil and gas reservoir, it will be in a high pressure state, so there must be a set of equipment that can control and adjust the oil and gas production, which is called wellhead equipment. It is mainly composed of casing head, tubing head and Christmas tree, which is used to control the flow of oil and gas.
The casing head is located at the lowest end of the whole Christmas tree, connecting all layers of casing in the well, thus sealing the annular space between all layers of casing. The tubing head is installed on the casing head, and its function is to hang the tubing in the well and seal the annular space between the tubing and the casing in the oil layer. At present, the jacking valve suspension method is widely used, that is, a jacking valve is installed on the casing cross, and there is a conical channel with a big top and a small bottom in the jacking valve. The tubing hanger is also a cone with a sealing ring. Under the tension of tubing weight in the whole wellbore, tubing hanger is firmly seated on the seat of jacking valve. The function of the jacking thread is to prevent the tubing string from being pushed out when the pressure in the well is too high. Christmas tree, some people think it is a tree. In fact, it is a conventional name for wellhead equipment in the industry. It was originally named because it looks like a Christmas tree. It consists of a gate, a four-way valve and a choke valve. Its function is to adjust the output of oil and gas wells by opening or closing the gate and adjusting the size of the nozzle, and it is connected with the ground oil collection pipeline.
Top thread flange 1- Schematic diagram of tubing hanging; 2- Top wire flange; 3- tubing hanger; 4.7— Sealing ring; 5- terminal filament; 6- capping; 8— Steel ring groove
Oil well-oil and gas channel from reservoir to surface 0 1