The main purpose of oil testing is to determine whether there is industrial oil and gas flowing in the test layer and obtain data representing its original appearance, but the purpose and task of oil testing are different in different stages of oilfield exploration. To sum up, there are four main points: a well is handed over for oil testing after drilling, and the oil testing team must do a good job of well condition investigation after receiving the oil testing plan, and can not start work until the derrick is erected, roped, connected and measured tubing is put in. General conventional oil testing, relatively complete oil testing procedures include drifting, well killing (well washing), perforation, string running, injection replacement, induced injection and drainage, production demand, pressure measurement, well sealing and return. When there is no oil and gas flow or low productivity after induced injection and drainage in a well, it is generally necessary to take stimulation measures such as acidification and fracturing.
1. drifting
Before testing an oil well, it is usually necessary to run an oil well meter. The outside diameter of the drift gauge is less than the inside diameter of the casing 6 ~ 8 mm, and the length of the big end is required to be not less than 0.5m m. Generally, it should be 50m below the bottom boundary of the perforated oil layer, and the new well should be connected to the artificial bottom hole. Old wells and wells with special requirements should be designed and constructed according to the process.
2. Good killing and good washing
(1) kill well
The purpose of well killing is to suppress the downhole oil layer so that it will not blow out during perforation or operation, and ensure the safe and smooth operation of oil testing and operation. At the same time, it is necessary to ensure that the reservoir will not be polluted and damaged due to well killing after construction. If the density of killing fluid is too high or a large amount of killing fluid leaks into the reservoir, it will affect the normal production of the reservoir and prolong the drainage time. In severe cases, the reservoir will be blocked and the reservoir will not produce oil. If the density of killing fluid is too low to hold the reservoir, it will cause blowout during construction. Therefore, attention should be paid to the reasonable selection of the density and mode of well killing fluid in the construction, so that the well killing work can truly achieve "pressing without death, living without spraying, spraying without leakage, and protecting the oil layer".
① Selection of killing fluid
Calculate the density of killing fluid according to the stable static pressure value of oil layer.
In the oil testing operation of new wells, the well can be killed according to the mud density when drilling the oil layer.
② well killing method
The commonly used well killing methods in the field mainly include perfusion method, circulation method and extrusion method.
Injection method: a section of killing fluid is injected into the well to hold the well down. It is used in oil testing in some low pressure and low production reservoirs.
Circulation method: This method is widely used in the field. It pumps the prepared killing fluid into the well for circulation, and displaces the high-density fluid into the wellbore, thus blocking the well. Circulating well killing method can be divided into positive circulation and reverse circulation according to different liquid inlet methods. The advantage of positive circulation well killing is that the back pressure to the reservoir is small and the pollution to the reservoir is relatively small. The disadvantage is that for wells with high oil-gas ratio, gas wells and high production wells, the killing fluid is easy to gas soak, which leads to the failure of killing. Reverse circulation well killing is generally used in the field, especially in high pressure and high production wells. First, circulate clean water, and then reverse circulate mud with large displacement. When the mud enters the tubing shoe, control the wellhead until the performance of the imported and exported mud is consistent, so that the well killing is easy to succeed at one time. The disadvantage of reverse circulation is that it has great back pressure on oil and gas reservoirs and serious pollution to oil reservoirs. If circulation is blocked during construction, it is forbidden to jump hard and squeeze mud into the oil layer.
Squeezing method: this method is often used in the case that the circulation cannot be formed in accident wells or non-tubing wells. The method is to pad with clean water first, and then squeeze with mud. Mud squeezing depth should be 50m above the top of oil layer. Shut in the well for a period of time after squeezing cement, then start the well and blow out, and observe the killing effect. Repeated extrusion must be carried out after the previous extrusion mud is sprayed clean.
(2) well washing
Well washing is to run the tubing into a certain depth, and then pump the well washing liquid into the well, so that the annular space between the tubing and the casing forms circulation, constantly washing the borehole wall and the bottom hole, taking the dirt out of the ground and ensuring the cleanliness of the wellbore and the bottom hole. Wash the well before well killing perforation, fracturing or acidizing and other stimulation measures, before cement plug (ash injection), when sand is buried in the oil layer or there is a lot of gravel at the bottom of the well.
Well washing methods usually adopt positive circulation and reverse circulation. The positive circulation well washing is strong, and it is easy to wash away the dirt and gravel at the bottom of the well, but the return speed of well washing fluid in the annulus is slow, so the ability to carry dirt is small. Reverse circulation is opposite to normal circulation, with weak washing ability and strong dirt carrying ability. However, the back pressure to the reservoir is large, which is not conducive to reservoir protection.
According to the specific conditions and design requirements of oil wells, which well washing method is better. Sometimes positive and negative circulation are combined to wash wells alternately. Positive circulation washes away mud, sand and cement blocks deposited at the bottom of the well, and then reverse circulation takes out dirty things.
The process of well washing is the same as well killing, so we should pay attention to possible phenomena, analyze and judge in time, and formulate corresponding measures. If a large amount of leakage is found during well washing, well washing should be stopped immediately.
Step 3 punch holes
Perforation is a downhole process in which a special downhole perforator is sent into the casing through cable or tubing, penetrating the casing and the cement ring outside the casing, and penetrating into the formation to a certain depth.
The purpose of perforation is to establish a flow channel between the formation and the borehole so that the formation fluid can enter the well.
Commonly used perforation methods include ordinary perforation, through tubing perforation and cableless perforation. The commonly used perforators in Shengli Oilfield are 57- 103, 73, 85, 5 1 and SSW-78 tubing barrels produced in Shengli Oilfield.
(1) common perforation
This perforation mode is relative to the injection hole through the tubing. It is a method of taking out the tubing in the well after killing the well and then running the perforator to perforate the casing. Commonly used gun types are 57- 103, 85, 73, etc. The perforation depth is determined according to the oil layer and casing coupling.
When ordinary perforation is used, the wellbore must be filled with killing fluid. Before perforation, a blowout preventer, such as a blowout preventer, must be installed.
(2) through the injection hole of tubing.
Tubing perforation is a kind of perforation technology without killing well. The tubing with a bell mouth at the lower end above the required perforated interval, and then the perforator is lowered from the tubing, and then it enters the position of the oil-bearing interval through the bell mouth for perforation.
When the ejection hole of tubing is used, the wellhead is equipped with a hydraulic blowout preventer, which does not need mud to kill the well. Generally, negative pressure perforation can be realized, and the pollution of medium pressure well fluid in perforation to the oil layer can be reduced. For some low-pressure reservoirs, in order to realize negative pressure perforation, the method of reducing the liquid column in the well can be adopted. The hydrostatic column pressure is lower than the formation pressure, thus realizing negative pressure perforation.
Ejection holes penetrating the tubing are adopted, and the bottom of the tubing must be provided with a bell mouth, the outer diameter of which is not less than 100mm, the inner diameter is 85 ~ 90 mm, and it must be smooth. The tubing is lowered to 30 ~ 50m above the short casing near the oil layer.
(3) Non-cable perforation
Wireless perforation, also known as tubing conveying perforation, is a method of perforating with perforator at the end of tubing string (TCP for short). Its principle is to connect all the perforators with guns in series at the end of the pipe string according to the depth and position of the oil and gas layer to be perforated in the oil well, so as to form a hard connection pipe string and run it into the well. Determine the perforated interval by measuring the radioactive curve of tubing or positioning sub, and then detonate. In order to realize negative pressure perforation, before initiation, the liquid column pressure in the perforation section can be lower than the formation pressure by lowering the liquid level in the well or opening the port valve under the packer in advance to protect the perforated oil and gas reservoir.
4. Run the pipe string
After perforation opens the oil layer, the test string should be run in time. According to the different requirements of downhole conditions and construction design, several kinds of pipe strings, such as optical tubing, packer and tester, are used in the pipe string structure.
(1) Smooth tubing string
The bottom of polished tubing should be equipped with a cross or anti-drop working cylinder. The design requires that the bottom of tubing should provide a bell mouth for wells using tubing injection holes. In general, the depth of tubing should be completed in the middle and upper part of oil layer. When the perforation thickness is very small, it can be completed at the top of the oil layer. Usually, the tubing for open hole completion is completed at the bottom of the casing shoe.
(2) Packer string
① Single packer string oil testing
There are two kinds of pipe string structures used in the field: one is to conduct single-layer oil testing with a single packer with a sieve tube, the packer is stuck between the reservoir to be tested and the reservoir to be tested, the bottom of the pipe string is plugged, and the sieve tube is aimed at the reservoir. The other is to test two layers with a single packer and distributor, and to test two layers with a fishing plug.
(2) Separate layer test of double packer string.
Run the secondary packer, divide the perforated layer into three layers, and test the fishing plugs of the three oil layers respectively.
In addition to the above two packers, the tubing string can be tested by layers, and the third packer can test three or four oil layers respectively. Because the salvage process is troublesome, oil fields are rarely used.
Requirements for running depth of pipe string: No sand layer is expected to be produced, and distributors at all levels are lowered to the middle or top of oil layer. It is expected that the sand layer may be produced, the packer should be as close as possible to the bottom boundary of the test layer, and the distributors at all levels should be directly above the packer.
③ Formation test string
Install various instruments and test tools, and connect them into the well in the order of test string. When tripping in, lift gently and release slowly. It is forbidden to release the brake suddenly to prevent the packer from setting in the middle and ensure that the test valve is always closed.
After running the pipe string to the preset position, install the wellhead control head and the surface pipeline, and set the packer with pressure.
Seduction and spraying
Whether it is a perforated well or an open hole well, mud or other killing fluids are usually injected into the well before oil testing, so there is no oil and gas flow between the oil layer and the bottom hole. Only after induced injection and drainage, the back pressure of the liquid column in the well to the oil layer is reduced, and the pressure difference between the oil layer and the bottom hole is formed, can oil and gas flow into the well from the oil layer, and can production, pressure measurement and sampling be carried out.
The commonly used methods of induced injection and drainage include injection displacement, swabbing, gas lift, mixed drainage and blowout. No matter which method is adopted, its essence is to reduce the Wainai liquid density of the liquid column height.
(1) Replace the spray
Displacement injection is a method to replace the high-density liquid in the well with the low-density liquid, thus reducing the pressure of the liquid column in the well. Under normal circumstances, clean water is often used instead of mud in the field, and sometimes light oil is used instead of injection to protect the oil layer. There are primary spray replacement method and secondary spray replacement method.
(1) Run the tubing to about 1m above the artificial bottom hole by one-time replacement method, replace the mud with clean water at one time, and then lift the tubing to the middle or upper part of the oil layer. This method is only suitable for oil wells with weak flowing ability, and there is still a gap between the replacement of clean water and the flowing of oil wells, so as to lift the tubing in time.
(2) During the second water injection, firstly, run the tubing to about 1m above the artificial bottom hole, replace the mud above the top of the oil layer with a section of clear water, then lift the tubing to the middle of the oil layer to install the wellhead, and finally replace all the mud above the top of the oil layer with clear water. This method is suitable for replacing high-pressure oil wells that can inject themselves after injection.
(2) Swabbing
When the oil well still can't flow by itself after injection, swabbing method can be used for injection and drainage.
Swabbing refers to using a special sucker rod to move up and down in the well through wire rope. When lifting, the liquid above the sucker rod is discharged from the wellhead, and at the same time, low pressure is generated at the lower part of the sucker rod, so that the oil layer liquid flow is continuously replenished into the well. When swabbing, the winch is used to wind the steel wire rope, which passes through the ground crane and crown block, and then is connected with the rope cap and weighting rod, and the weighting rod is connected with the sucker rod to form a swabbing system.
Pumps used for swabbing in Shengli Oilfield are mainly two-lobe pumps.
(3) gas lift
After fresh water injection, the oil well still can't inject itself. Gas lift can also be used to induce spraying. Gas lift method is to inject compressed gas into tubing or casing by air compressor, so that the liquid in the well can be discharged from casing or tubing.
(1) The ordinary gas lift method is divided into positive lift and negative lift. Lifting is the use of compressor to inject high-pressure compressed gas from tubing, and liquid returns from casing. Reverse lifting means that high-pressure compressed gas enters from the annulus of oil casing and liquid returns from oil pipe.
(2) Gas lift hole gas lift method In order to speed up drainage, gas lift hole gas lift method can be used for oil testing in deep wells. Gas-lift hole gas-lift method is to lift the liquid in the well by stages according to the well depth and liquid level height, as well as the displacement and working pressure of the air compressor, with different small diameter pups at different depths of the tubing. During construction, a blower is used to inject high-pressure compressed gas into the casing. When the compressed gas reaches the depth of the gas lift hole, a part of the gas enters the oil pipe from the small hole, which reduces the density of the liquid mixture in the oil pipe. At the same time, a part of compressed gas continues to descend to replace the liquid in the casing. When the gas mixture in the tubing reaches a certain level, the liquid is ejected by the gas flow, so that the wellbore liquid is discharged step by step.
③ The gas lift plus swabbing method uses casing gas lift and tubing swabbing at the same time, and the mixed drainage method of lifting and swabbing is also an effective drainage method on site. Pay attention to pumping and continuous drainage when using; When the well is shallow and the pipe string has gas lift holes, pay attention to prevent jacking accidents during lifting.
(4) Air mixed water discharge
Mixed gas drainage is to reduce the back pressure at the bottom of the well by reducing the density of liquid column in the wellbore. The method is to use blower and cement truck to inject gas and pump water into the casing at the same time to replace the liquid in the well. Because the ratio of gas volume to water volume is different, the density of injected mixed gas water is also different. The density is injected step by step from large to small, and the back pressure at the bottom of the well gradually decreases, thus establishing enough pressure difference between the formation and the bottom of the well to induce oil flow.
5] Blow out
After the fluid is discharged, the well can be blown away. The purpose of blowout is to eliminate the fluid in the wellbore, make the reservoir smooth and realize normal oil production. According to the reservoir productivity, wellhead gate or choke can be used for control, and oil casing can be reversed for blowout. If sand is found in the reservoir during blowout, a choke should be installed immediately to control it. The eligibility criteria for blowout are:
(2) Non-flowing production wells.
For non-flowing wells, according to the different liquid supply capacity and fluid properties of oil layers, swabbing and gas lift can be used to obtain production.
(1) swabbing production: swabbing is carried out at a fixed depth, time and times according to the liquid supply capacity of the formation, so as to keep the dynamic liquid level at a certain depth all the time. In this way, stable oil-water output and oil-water analysis samples were obtained continuously for two days, and the fluctuation range of output was less than 20%.
(2) Production gas lift. After running the tubing at a certain position, gas lift with fixed depth, fixed time and constant pressure is adopted to obtain the produced fluid of the oil layer. The gas lift cycle is determined by the liquid supply capacity of the reservoir. Continuously obtain the output of more than two daily cycles.
For heavy oil wells, the tubing can be lifted to a certain position, and hot water can be used to replace crude oil for metering, and then the water above the tubing shoe can be hollowed out by a blower, and then the crude oil can be replaced for metering after the liquid level rises, so that the output of three cycles can be continuously injected. This method can only get the approximate production, and it is impossible to determine whether the formation is watered or not.
(3) Low-yield wells seek production.
Low-yield wells refer to wells below the industrial oil flow standard. Due to the poor liquid supply capacity of the formation, it is difficult to use the above non-flowing wells to seek production. This kind of well generally requires that the liquid level be reduced to the required hollowing depth after mixed drainage and pumping, and the productivity can be determined by sampling the liquid level at the bottom of the well.
(1) Calculate the liquid production according to the liquid level rise.
(2) Carry out underground sampling to realize water-based.
③ backwashing well to measure oil production.
7. Pressure measurement
Pressure measurement is an important part of the test. After flowing well production is qualified, run the manometer to measure flowing pressure, then shut in the well to measure pressure recovery, and stop measuring static pressure after the pressure is stable, otherwise run the manometer to make up static pressure. According to the requirements, the wellhead pressure of non-flowing wells should be stabilized before or after production, and the static pressure of oil layer should be measured by pressure gauge.
8. Closed loop
If a well testing layer needs to be closed and returned to other horizons after oil testing, the return mode can be determined according to the downhole situation and scheme requirements. In general, downhole packers should be used as much as possible. In addition, the commonly used sealing methods include ash injection, sand filling and bakelite plug, bridge sealing, cable bridge plug and so on.
Ash injection is the most commonly used water sealing method in layered oil testing at present. The method is to lower the tubing to the bottom boundary of the expected cement plug, replace the calculated cement slurry to the expected position, and then lift the tubing to the surface of the expected cement plug for reverse circulation to wash away the excess mortar. Finally, lift the tubing and shut in the well for solidification.
In order to ensure the construction safety and improve the success rate of ash injection, it is required that the underground is clean, the liquid level is stable and there is no gas leakage. Mortar is prepared in strict accordance with the test formula and mixed evenly. The liquid used to replace mortar should be consistent with the density of the liquid in the well and should be accurately measured. After replacing the cement slurry, the tubing should be lifted to about 1m above the required cement plug surface for reverse circulation well cleaning. After backwashing, at least 50 meters (5 pipes) should be lifted. In general, the pocket after ash spraying shall not be less than 10m. During pressure test, clean water is pressurized to 12MPa, or mud is pressurized to 15MPa, and the pressure drop is less than 0.5 MPa within 30 minutes.