The vertical borehole is drilled vertically, reaching the target layer within the specified dip angle and azimuth angle, and there are certain requirements for borehole curvature and horizontal displacement of the bottom hole relative to the wellhead (Figure 1). Excessive horizontal displacement at the bottom of the production well will disrupt the well layout scheme of oilfield development; The horizontal displacement at the bottom of the exploration well is too large, and the expected target layer may not be drilled. Excessive well full angle change rate will increase the difficulty of drilling and oil production and easily lead to downhole accidents. The factors affecting angle of inclination and azimuth are: geological conditions, drilling tool assembly, drilling technical measures, operation technology and equipment installation quality. In order to prevent angle of inclination and borehole curvature from being too large, a reasonable BHA must be selected. There are two common types: rigid hole drilling assembly (Figure 2) and pendulum drilling assembly (Figure 3). The former can use larger WOB drilling, which is beneficial to improve ROP, and the borehole curvature is small, but it cannot be corrected. The latter needs to control a certain WOB to improve the penetration rate, but it can be used to correct the deviation.
Directional well is a well drilled to the target horizon along the pre-designed drilling direction (inclination and azimuth). Mainly used for: ① limited by the ground topography, such as oil fields buried under towns, mountains, lakes or fertile fields; ② offshore cluster drilling; (3) Due to special geological structures (such as faults, fractured layers or excessive dip angle). ), drilling directional wells is beneficial to the exploration and development of oil and gas reservoirs; ④ Handling downhole accidents, such as sidetracking and rescue wells drilled to prevent blowout from catching fire.
Directional well profile design generally consists of vertical section, deflecting section, stable section and inclined section. Inclined drilling tools composed of bent joints of downhole power drilling tools (turbine drilling tools or screw drilling tools) are often used to deflect and twist well sections (Figure 4). When the deviation finally reaches or approaches the level, it is called a horizontal well. During directional drilling, the inclination and orientation of the borehole must be monitored frequently, and the borehole trajectory map should be drawn at any time for timely adjustment. Commonly used inclinometers include single-point and multi-point magnetic camera inclinometers and gyro inclinometers. In recent years, inclinometer while drilling has also been used to know the inclination and orientation of borehole at any time without tripping out. According to the signal transmission mode, there are two kinds: wired and wireless. The former uses cables to transmit signals, while the latter uses mud pulses, electromagnetism and sound waves.
Cluster wells, also known as dense wells and grouped wells (Figure 5), are used to drill several to dozens of directional wells from different directions in a location and limited well site, so that each well can reach the target layer along its own design well axis. It is usually used in offshore platforms or cities, fertile fields, swamps and other areas, which can save a lot of investment, occupy less land and facilitate centralized management.
In jet drilling, high-pressure mud delivered by mud pump forms high-speed impact jet (generally above m/s), which directly acts on the bottom of the well, making full use of hydraulic energy (generally more than 50% of pumping power acts on the bottom of the well), so that drilling cuttings can be washed away from the bottom of the well in time or directly break the formation, which can greatly improve the drilling speed. The reasonable working mode is to adopt higher pump pressure, lower displacement and smaller bit nozzle diameter.
Based on the analysis of drilling data and optimization of drilling parameters, various controllable factors (such as bit type, WOB, rotation speed, mud performance, hydraulic factors, etc.) are analyzed by means of electronic computer and optimization method. ) and other factors affecting drilling speed, and compiled a calculation program. Optimize the cooperation to make the drilling work achieve high quality, high speed and low cost.
Comprehensive analysis data of formation pore pressure prediction and balanced pressure drilling (ROP, shale density, mud specific gravity, temperature, etc. ) During earthquake, logging and drilling, predict formation pore pressure, judge possible abnormal pressure formation, and take timely measures to prevent sudden downhole complications such as blowout, lost circulation and well collapse. According to the known formation pore pressure and formation fracture pressure, the reasonable mud specific gravity and casing program are determined. When the mud column pressure in the well is roughly balanced with the formation pore pressure, drilling is called balanced pressure drilling. It can significantly improve the penetration rate and is also beneficial to the discovery of oil and gas reservoirs.
Well control technology When drilling an abnormally high pressure formation and mud gas invasion or well kick occurs, calculation methods and corresponding technical measures are adopted to adjust the mud specific gravity and flow characteristics, and hydraulic high-pressure blowout prevention equipment is used to control and eliminate the overflow in the well and prevent blowout.
According to the design requirements, rock samples (cores) of required horizons are drilled from underground to obtain original data for oil and gas exploration and development. Common coring tools are mainly composed of coring bit, core barrel, core claw and joint. During coring drilling, the drill bit keeps cutting the rock at the bottom of the well annularly, so that the drilled columnar core keeps entering the core barrel. In order to meet the special needs, there are sealed coring, pressure-keeping coring and coring tools (rubber coring tools) for extremely loose and broken strata.