Causes and Solutions for Drillpipe Sticking in Oil Drilling
Causes and Solutions for Drillpipe Sticking in Oil Drilling
Blog Article
Drill stuck means that the drill cannot move freely in the well for a long time due to geological factors, poor drilling fluid performance, improper technical measures, etc. during the drilling process. This phenomenon is called drill stuck. The main causes include drill stuck by adhesion, drill stuck by sand, drill stuck by sand bridge, drill stuck by well collapse, drill stuck by reduced diameter, drill stuck by mud pack, drill stuck by falling objects, and drill stuck by drill falling off.
Remedial Actions for Drill Sticking Incidents
When drill sticking occurs, several methods can be employed to resolve the issue:
- Soaking in oil to release the stuck.
- Using a jar to release the stuck.
- Inverted casing milling.
- Explosive loosening.
- Explosive drilling of new holes by side drilling with drill tools, etc.
Understanding Well Cementing
Well cementing is to lower a certain size of casing string into the well and inject cement slurry around it to fix the casing to the well wall to prevent the well wall from collapsing. Its purpose is to: isolate loose, easy to collapse, easy to leak and other complex formations; isolate oil, gas and water layers to prevent mutual leakage; install wellheads to control oil and gas flow to facilitate drilling or oil and gas production.
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Components of Well Body Structure
The well body structure includes:
- The casing layers of a well.
- The diameter and insertion depth of each layer of casing.
- The corresponding drill bit diameter and drilling depth of each layer of casing.
- The cement return height outside each layer of casing, etc.
Lower Structure of Casing String
The lower structure of the casing string consists of:
- Guide shoe: guide casing into the well to avoid casing insertion or scraping the well wall.
- Casing shoe: guide the drilling tool inside it into the casing.
- Swirl nipple: make the cement slurry swirl upward, which is conducive to replacing mud and improving the quality of cementing.
- Casing back pressure valve: prevent cement slurry from flowing back and prevent mud from entering the casing during casing lowering.
- Support ring: support rubber plug and control the height of cement plug.
- Casing centralizer: make the casing centered in the well and improve the quality of cementing.
Cementing Construction Process
The cementing construction process involves the following steps:
Lower casing to the predetermined depth → install cement head, circulate mud, connect to the surface pipeline → inject spacer fluid → inject cement → push rubber plug → replace mud → impact pressure → end cementing and wait for setting.
Wellhead Device for Completion
The wellhead device for completion includes:
- Casing head - seals the annulus between two layers of casing, suspends the second part of the casing string and bears part of the weight.
- Tubing head - supports cone pipe hanger, connects oil layer casing and Christmas tree, blowout gate, pipeline.
- Christmas tree - controls the flow of oil and gas, conducts production safely and in a planned manner, and performs completion testing, fluid injection, well killing, oil well cleaning and other operations.
Tail Pipe Cementing Method
Tail pipe cementing is a cementing method in which only the newly drilled open hole section in the lower part of the well with casing already installed in the upper part is cemented by injecting cement into the casing. There are three ways to fix the tail pipe: tail pipe seated at the bottom of the well; cement ring suspension method; tail pipe hanger suspension method.
Oil Testing Procedures
After drilling and discovering oil and gas layers, it is necessary to make the oil and gas in the oil and gas layers flow from the bottom of the well to the ground, and obtain dynamic data such as oil and gas layer production and pressure, as well as oil, gas and water properties through testing, which is called oil (gas) testing.
Perforation Techniques
When drilling is completed, it is necessary to lower the casing and inject cement to fix the well wall, and then lower the perforator to shoot the casing and cement ring until the oil (gas) layer to open a channel for oil and gas to flow into the wellbore, which is called perforation. At present, the perforators widely used at home and abroad are bullet-type perforators and energy-gathering jet perforators.
Understanding Bottom Hole Pollution
Bottom hole pollution, also known as bottom hole damage, refers to the phenomenon that the permeability of the formation near the wellbore is reduced due to the loss of drilling fluid or the leakage of filtrate of water-based drilling fluid into the formation during the drilling or repair process of the oil well.
Induced Blowout Process
Before perforating, in order to prevent blowout accidents, oil and gas wells are generally filled with well-killing fluid. After perforating, in order to guide the liquid in the formation to the ground, it is necessary to reduce the liquid column of the well-killing fluid and reduce the pressure on the fluid in the formation. This process is a process in the oil testing work, called induced spraying. The methods of induced spraying include replacement spraying, suction, bailing, gas lift, etc.
Advanced Testing Methods
Drill Stem Formation Test
Drill stem formation test is an advanced technology that uses drill stem or tubing to lower a formation tester with a packer into the well for oil testing. It can be tested in wells with casing or in open holes without casing; it can be tested after drilling is completed or in the middle of drilling.
Cable Formation Test
After oil and gas are found during the drilling process, a cable is used to lower the formation tester to obtain samples of the fluid in the formation and measure the formation pressure, which is called cable formation test. This test method is relatively simple and can be performed repeatedly.
Tubing-Transmitted Perforation
Tubing-transmitted perforation is an advanced technology that uses tubing to carry the perforator downhole. After perforation, the fluid in the formation can be directly led to the surface through the tubing, without the need to inject a large amount of well-killing fluid into the well during perforation to avoid bottom hole pollution.
Key Rock and Fluid Properties
Rock Porosity
The porosity of a rock refers to the ratio of the volume of space Vp not filled by solid matter in the rock to the total volume Vb of the rock. It is represented by the Greek letter Φ, and its expression is: Φ=Vpore/Vrock×100%=Vp/Vb×100%
Formation Crude Oil Volume Coefficient
The formation crude oil volume coefficient βo, also known as the underground volume coefficient of crude oil, or simply the crude oil volume coefficient. It is the ratio of the volume of crude oil underground (i.e., the volume of formation oil) to its volume after degassing on the ground. The underground volume coefficient βo of crude oil is always greater than 1.
Fluid Saturation
The saturation of a certain fluid refers to: the volume percentage of a certain fluid in the pores of reservoir rocks. It indicates the degree to which the pore space is occupied by a certain fluid. If the pores in a rock are filled with several phases of fluid, the sum of the saturations of these phases of fluid is 1 (100%).