Drill Bit Usage Data

1. Formation Lithology

The lithology and hardness of the formation are different, and the rock crushing mechanism is different, which causes the drill bit failure in different forms. The rock physical and mechanical properties of the common formation lithology in drilling in various oil fields in my country have been measured. According to the formation lithology collected on site and the drilling time record of each meter of lithology, the hardness, plasticity, brittleness, abrasiveness and drillability of the formation rock are analyzed, and the drill bit selection and use are confirmed to be reasonable by comparing the failure form of the drill bit.

2. Well section position

The mechanical properties of rocks in different positions in the crust vary greatly. Deeply buried rocks are in a state of multi-directional compressive stress, which reduces the rock pores and increases the strength. The upper well section generally has loose cementation and soft rocks, high drill bit speed and low drilling pressure. The lower well section generally has hard rocks and high abrasiveness, low drill bit speed, high drilling pressure and long service life. According to the collected well section location and the drilling time record of each meter of lithology, the hardness, plasticity, brittleness, abrasiveness and drillability characteristics of the formation rock are analyzed, and the drill bit failure mode is compared to confirm whether the drill bit selection and use are reasonable.

3. Wellbore structure

Different wellbore structures have special requirements for the size, model and use of the drill bit. For example, the deflection drill bit is generally required to have trimming teeth or a diameter protection structure, and the use requires high speed and low drilling pressure. Collect information on wellbore structure and drill bit selection, use parameters, etc., and confirm whether the drill bit selection and use are reasonable according to the drill bit failure mode.

4. Drilling parameters

The determination of drilling pressure and speed not only determines the efficiency of the drill bit in crushing rocks, but also affects the wear of the drill bit teeth and bearings. In shallow wells and soft formations, the drill bit is mainly shearing, and generally uses high speed and low drilling pressure. In medium-hard formations, the drill bit produces a comprehensive effect of shearing, impacting, and crushing, and generally uses medium speed and medium or high drilling pressure. In deep wells and hard formations, the drill bit is mainly crushing and impacting, and generally adopts higher drilling pressure and low rotation speed. The reasonable selection of drilling parameters largely determines the failure mode of the drill bit. Collect shift reports and weight table records, analyze the drilling parameters used and their changes, and determine the rationality of use according to the failure mode of the drill bit.

5. Mud performance Jet drilling requires mud to have:

1) low water loss, low sand content, appropriate shear force and pH value, which can effectively protect the well wall and suspend rock cuttings;

2) low specific gravity and low viscosity, which can reduce the pressure and power loss of the circulation system;

3) can effectively carry rock cuttings at low return speed;

4) have good shear dilution characteristics. Different geological conditions of the formation, different types of mud and related properties are selected, which affect the coordination of drilling pressure, rotation speed, hydraulic parameters and failure mode of the drill bit. Mud performance is an important factor in drill bit wear. For example, sand content in mud has a great influence on drill bit flow channel erosion.

6. Mud parameters

The mud displacement, cylinder sleeve diameter, nozzle diameter, model and combination used in drilling different well sections are of practical significance for selecting the drill bit pressure drop and drill bit water horsepower. Jet drilling causes damage to the drill bit flow channel while strengthening the hydraulic effect of the drill bit. Mud parameters and change records are important basis for drill bit failure analysis. For example, failure of drill bit flow channel erosion, erosion of cone matrix causing tooth loss and broken teeth are directly related to mud parameters.

7. Drill string assembly

The drill string is the hub connecting the ground and the well. Different drill string structures and stress states in the well determine the size and direction of the drilling pressure on the drill bit. For example, when directional drilling or the well deviation is large, the actual drilling pressure on the drill bit is smaller than the data displayed on the drilling pressure gauge. If the drill string assembly is equipped with a centralizer, the actual drilling pressure is even smaller. At the same time, due to the friction between the centralizer and the well wall, the working stability of the drill bit is enhanced, which is conducive to the use of the drill bit.

8. Drill bit quality

Drill bit quality is the basis of drill bit use. Checking the quality and newness of the drill bit and the reliability of the nozzle installation before entering the well is crucial to the use of the drill bit. Checking the quality record of the drill bit before entering the well can distinguish whether the drill bit failure is due to quality or use.

9. The previous drill bit

The failure of each drill bit affects the environment at the bottom of the well and the use of the next drill bit. Collecting the failure description record of the previous drill bit and analyzing the failure cause of the previous drill bit can determine the use environment of the drill bit used in the well and judge the impact of the well falling objects, well diameter, bottom shape, etc. on the failure of the drill bit.

1. Knowledge related to the use of drill bits

(I) Formation lithology

The stratum is composed of rocks, which are mainly composed of more than a dozen minerals such as quartz, feldspar, mica, calcite, clay minerals, etc. According to the origin of the rock, it is divided into three categories: igneous rock, metamorphic rock and sedimentary rock.

1. Types and characteristics of stratigraphic lithology

Clay and loess: sedimentary rocks composed of clay mineral particles with a diameter of less than 0.01 mm.

Mudstone and shale: rocks formed by clay sediments through diagenesis. Blocky mudstones are shale, and thin flaky shale. Shales rich in petroleum bitumen and used to extract petroleum are oil shale.

Sandstone: rock formed by sand particles cemented together. Coarse sandstone with a diameter of 0.5~1 mm, medium sandstone with a diameter of 0.25~0.5 mm, fine sandstone with a diameter of 0.1~0.25 mm, and siltstone with a diameter of 0.01~0.1 mm. According to the different cementing materials, sandstone is divided into siliceous, calcareous, etc. Sandstone has pores and can store fluids. Sandstone with large pores and limestone with developed cracks are rocks with good permeability.

Conglomerate: rock particles larger than 1 mm are called gravel. Rocks formed by gravel and cement are called conglomerates. According to the size of the gravel, it is divided into three types: coarse conglomerate, medium conglomerate and fine conglomerate. Those with different shapes and edges are called breccia.

Limestone: The main component is calcium carbonate. It is formed in the ocean or onshore lakes by chemical sedimentation. It is blocky, relatively dense and hard. According to different components, limestone can be divided into limestone, marl, sandy limestone, mud limestone, dolomite and shell limestone (depositional diagenesis of biological shells). Mud-containing limestone has greater plasticity, and pure limestone is brittle and hard.

2. Drillability and classification of formation rocks

The drillability of rocks is the basic factor that determines the drilling efficiency. It reflects the difficulty of rock crushing during drilling and is the basis for the reasonable selection of drilling methods, drill bit structure and drilling procedure parameters. Analyzing the drillability of formation rocks encountered by the drill bit can understand the rationality of drill bit selection and its adaptability to the formation. Generally, the product of the mechanical drilling speed and footage of the drill bit is used as a measurement indicator.

The basic properties of rocks that affect rock drillability include: rock mineral composition and structural structure, density, porosity, water content and permeability; mechanical properties include hardness, strength, elasticity, brittleness, plasticity and abrasiveness. Generally, when there is a lot of quartz in the rock-forming minerals, the cementation is firm, the particles are fine, the structure is dense, and there is no weathering and alteration, the rock drillability is poor; while the hardness and strength of the rock are high and the abrasiveness is strong, the rock drillability is poor.

The process factors that affect rock drillability include: the pressure applied to the drill bit, the rotation speed, the mud type and the bottom of the well.

The technical conditions that affect rock drillability include: drilling equipment, borehole diameter and depth, drilling method, structure and quality of rock breaking tools, etc. There are four viewpoints on rock drillability classification, and there are also four classification methods. Due to the continuous improvement of process technology, the relative and absolute relationship between the drillability grades of various levels of rocks has also changed.

3. Collection of formation lithology data

The work of collecting formation lithology data during drilling is called logging. Therefore, the collection of formation lithology data should focus on the collection of original geological logging data

Sand sample logging: also known as cuttings logging. In new exploration areas, sand samples are generally taken once per meter, and production wells are generally sampled at the boundary of the formation or the standard layer, oil and gas layer. The lithology of the formation encountered during drilling can be determined through sand sample logging data.

Drilling time logging: Record the time required for each meter of drilling, draw a curve according to the depth of the well, and use it in combination with other data as a reference for judging the formation. The hardness of the formation directly affects the speed of drilling. By recording the speed of drilling, you can also understand the changes in the formation and the working conditions of the drill bit in the well.

Mud logging: The changes in mud properties during drilling are often related to the properties of the formation encountered. If the gypsum layer is encountered, the viscosity of the mud will increase, the water loss will increase, the calcium content will increase, and the sulfate ion will increase; if the oil and gas layer is encountered, a large number of oil flowers and bubbles will appear on the mud tank and pool, the viscosity will increase, and the specific gravity will decrease. The lithology of the formation encountered can be judged by mud logging data.

4. Formation lithology and drill bit use

The selection and use of drill bits are based on the mechanical and physical properties of the rock and the formation conditions. The rock properties closely related to the use of drill bits are: hardness, plasticity and abrasiveness.

The hardness of the rock refers to the ability of the rock to resist the pressure of the drill bit cutting parts. The hardness of the rock is related to the composition and size of the rock particles and the properties of the cement between the particles. The comparison levels are: Level 1-Talc; Level 2-Gypsum; Level 3-Calcite; Level 4-Fluorite; Level 5-Apatite; Level 6-Orthoclase; Level 7-Quartz; Level 8-Topaz; Level 9-Corundum; Level 10-Diamond. The higher the level, the greater the hardness and the slower the drilling speed.

The plasticity and brittleness of rocks are two opposing concepts. The property of an object that undergoes plastic deformation before destruction is called plasticity, and the property of an object that does not undergo plastic deformation before destruction is called brittleness. Objects with high plasticity have no brittleness or very little brittleness, and vice versa. Objects with high brittleness have no plasticity or very little plasticity. For rocks, they can be divided into three categories. The first category is brittle rocks that do not undergo plastic deformation before destruction, such as granite and quartz sandstone; the second category is plastic rocks that undergo large plastic deformation before destruction, such as mudstone; the third category is plastic-brittle rocks that break after showing small plastic deformation before destruction, such as mud-cemented sandstone. The abrasiveness of rock refers to the wear effect of rock and rock debris on the drill bit on the surface where the rock contacts the drill bit. The ability of rock to wear the drill bit is called the abrasiveness of rock, which is related to the composition, particle size and shape of the rock itself. The greater the abrasiveness of the rock, the more severe the wear of the drill bit, and the less the total footage of the drill bit. According to the wear per unit friction distance, various rocks are divided into 12 levels from small to large according to their abrasiveness. Level 1: mudstone and carbonate rock; Level 2: limestone; Level 3: dolomite; Level 4: siliceous rock; Level 5: ferromagnesian rock and low-abrasive rock containing 5% quartz; Level 6: feldspar rock; Level 7: feldspar rock containing more than 15% quartz and low-abrasive rock containing 10% quartz particles; Level 8: quartz crystalline rock; Level 9: quartz clastic rock, hardness PY ≥ 350Kg/mm2; Level 10: quartz clastic rock, hardness PY = 100~200Kg/mm2 and rock containing 10~20% quartz particles; Level 11: quartz clastic rock, hardness PY = 200~250Kg/mm2 and rock containing 30% quartz particles; Level 12: quartz clastic rock, hardness PY < 100Kg/mm2. Salt rock, mudstone and some sulfate and carbonate rocks are the least abrasive rocks when they do not contain quartz particles; limestone, dolomite and other rocks are low abrasive rocks; igneous rocks contain less feldspar and quartz, fine grain size, small hardness difference between minerals and low abrasiveness

5. The influence of formation lithology on drill bit failure

The influence of formation lithology on drill bit failure is reflected in the drilling process: affecting the drilling speed and drill bit footage; causing complex situations such as well leakage, blowout, well collapse and drill stuck during the drilling process; changing the mud properties; affecting the wellbore quality, such as well inclination and well diameter irregularity, and then affecting the cementing quality. By analyzing the formation lithology and its influence on the drilling process, the rationality of drill bit selection and use can be judged.

The influence of clay, mudstone and shale layers: It is very easy to absorb free water in the mud and expand, which reduces the well diameter, causing drilling resistance and even drill stuck. As the soaking time increases, the block will fall off and peel off, which will expand the well diameter and cause well collapse. Clean water or low-density and low-viscosity mud should be used as much as possible for drilling. Carbonaceous shale has weak connection and is prone to collapse. Mudstone is soft, has fast drilling speed, and is also prone to mud packing.

Sandstone: Its properties vary greatly depending on the size, composition, and cement of the particles. The finer the particles, the more quartz particles, and the more siliceous and ferrous cements, the harder it is, and the greater the wear on the drill bit, such as quartz sandstone; the more mud cements, the more mica and feldspar components, the softer and easier to drill; the coarser the particles, the less cement, the better the permeability, and the easier it is to produce mud permeability leakage, and form a thicker mud cake on the well wall, causing complex situations such as adhesion and stuck drill, resulting in abnormal use of the drill bit.

Conglomerate: Drilling in conglomerate layers is prone to drill jumping, stuck drill, and well wall collapse; when the pump displacement is small or the mud viscosity is low, the gravel particles are not easy to return, which causes greater damage to the drill bit cone body and teeth.

Limestone: Generally hard, slow drilling speed and less footage. Some have cracks and holes. When drilling into cracks and holes, it will cause drilling jams, emptying, mud loss, etc., and sometimes blowouts will occur after well leakage.

Limestone formations have a great influence on drill bit footage, mechanical drilling speed and drill bit failure. In addition, when the formation is soft and hard, such as mudstone and harder sandstone, it is easy to produce well deviation; well deviation is easy to produce when the formation inclination is large. The drill bit is easy to be damaged when drilling in an inclined well. When the rock formation contains soluble salts, such as gypsum layer, rock salt layer, etc., it will destroy the performance of the mud and affect the normal use of the drill bit.

(II) Drilling process

Generally refers to the three controllable process parameters in the drilling process: drilling pressure, rotation speed and mud displacement. In actual application, the drilling process should be formulated according to the formation conditions, drill bit type, drilling equipment and operator technical level. According to different requirements and conditions, drilling technology is divided into:

1) Optimized drilling technology: Under certain conditions, drilling technology parameters that can achieve the best economic indicators.

2) Enhanced drilling technology: In order to achieve a higher drilling speed, drilling parameters higher than general drilling parameters are used.

3) Special drilling technology: Special measures or restricted drilling parameters are used for special purposes.

Different drilling parameters require the use of drill bits of different specifications and models. The failure forms of drill bits during drilling also have their own characteristics and should be treated differently.

1. The influence of drilling pressure on drilling

Drilling pressure is a necessary condition for rock breaking at the bottom of the well. The size of drilling pressure determines the way and characteristics of rock breaking, and directly affects the drilling speed and the damage form of the drill bit. During drilling, the drill bit is subjected to axial pressure and rotational force. The cutting teeth are worn, blunted or damaged in the process of pressing into and shearing the rock, which will inevitably affect the drilling speed. With the increase of drilling pressure, the drilling speed will continue to increase, and the bearings and cutting teeth of the drill bit will also accelerate the wear, affecting the drilling speed. There are three different stages in the relationship between drilling pressure and drilling speed.

Surface crushing stage: When the drilling pressure is less than the rock penetration hardness, the cutting teeth cannot cut into the rock, and can only crush the rock in the form of friction on the rock surface, which causes greater wear on the cutting teeth. Although the drilling speed also increases proportionally with the increase of drilling pressure, the drilling speed is very low;

Fatigue crushing stage: When the drilling pressure is close to the rock penetration hardness, the cutting teeth do not cut into the rock, but many cracks are generated on the rock surface. After repeated action of the cutting teeth, volume crushing is also generated;

Volume crushing stage: When the drilling pressure is added to a value greater than the rock penetration hardness, the cutting teeth cut into the rock to produce volume crushing, and the drilling effect can be obvious, which is normal drilling. Therefore, the drilling pressure applied to the roller drill bit must meet the requirements that the cutting teeth can press into the rock to cause volume crushing of the rock.

By doubling the drilling pressure, the roller drill bit was tested to drill different grades of rocks. The results show that different rocks have different drilling speeds when the drilling pressure is increased. Among them, the medium-hard rock layer (rock)