I. Overview of the International Scientific Drilling Program
Under the framework of International Continental Scientific Drilling Organization (ICDP), more than 20 major international drilling projects have been organized and implemented. ICDP focuses on challenging research topics in earth science and international social and economic issues, such as continental dynamics and natural disasters, volcanic system and thermal state, earth history and climate change, tectonic collision, non-traditional energy sources, deep organisms and so on. Among them, the outstanding research results are as follows: (1) drilling cores in San Andes Mountain, California, Chelenburg, Taiwan Province Province, China, and Corinth Bay, Greece to study the basic process of earthquake cycle; Study on Volcanic Activity Process of Yunxian Volcano in Japan, Hawaii and Iceland Supercritical Volcanic Fluid: Paleogeological and Climate Evolution of Lake Titicaca, Malawi, Bosumtvi and Qinghai Lake: Formation process of craters in Hiksulubo, Bosumtvi and Chesapeake Bay under the impact of meteorites of different sizes and their impacts on the surrounding environment. The research topics of ICDP in the next few years include: climate dynamics and global environment, craters and their formation process, underground organisms, active faults, plate convergence edges and collision zones, natural resources and so on. In order to meet the challenge of future continental scientific drilling, drilling technology is a device to improve the in-hole safety drilling system, nondestructive and pollution-free coring in complex strata and long-term observation equipment in deep harsh environment.
During the four years from 2004 to 2008, the International Ocean Drilling Organization (IODP) completed the following investigations: it took 55 years to complete the historical record from greenhouse to ice room in Lomonosov Ridge, Arctic; Three observation wells were set up on the Fuka Ridge to investigate the submarine ocean current on the Juanshan side. Investigate the ultra-high pressure and ocean current processes under the deep water in the Gulf of Mexico; The bedrock data of Cox plate seabed were re-acquired by drilling.
Drilling equipment for deep-water drilling on hard ice is a necessary condition for human beings to carry out polar exploration activities efficiently. In the past, due to the lack of special ice-breaking drilling boats, many scientific research activities were slow or even impossible. For example, ODP voyage 15 1 started drilling in the highlands of Giermark. It was not until 55 years later in 2004 that the IODP ACEX expedition regained 40 feet at the top of Lomonosov Ridge at the bottom of the Arctic Ocean at 87 55'16 "north latitude and 39' east longitude. Recently, the world's most advanced polar exploration facility-the icebreaker "Northern Lights" (photo 1) was successfully built. Its drilling depth can break ice in the polar ocean covered with permanent ice with water depth of 80-5000m, and it can also be used for long-term international multidisciplinary Arctic drilling survey. The ship's hull design is novel, equipped with satellite navigation, azimuth propulsion system and ice handling support. The dynamic positioning system can operate on the ice layer with a thickness of more than 2.5 meters. Customized alpine deep-water drilling rig, fully enclosed drilling platform and pre-research studio allow scientific and technical personnel to work all day under polar conditions.
In order to better meet the special requirements of continental scientific drilling, ICDP entrusted German PFZ(Geo-Forsechungs Zentrum) to develop a new drilling rig-Innovalig (Figure 2). Compared with the standard oil drilling rig, this drilling rig has the following technical characteristics: rotary drilling, conventional coring, wireline coring and gas lift can be used for drilling; Modular drilling rig design has high safety standards, high automation and comprehensive power concept, and there is no big rope hydraulic lifting and feeding system, which reduces environmental pollution and noise intensity, reduces site and ground, and reduces drilling cost. The drilling rig is also equipped with logging instrument storage unit and logging cable guide, which can realize fast logging. Based on the principle of mass spectrometry, the drill cuttings sample collector and mud gas analyzer enable field research to be conducted in situ; The drilling information system has been integrated with ICDP drilling information system. The technical parameters of the drilling rig are: generator capacity 3× 1540 kVA, driving power 4000 kW, mud pump power 3× 1000 kW, drilling depth 5000m, nominal hook load 3,500 kN, rotating speed 220 rpm, torque 40 ~ 75kn·m, lifting cylinder stroke 22 m, rope taking.
Figure 1 "Northern Lights" research icebreaker
Figure 2 German innovative drilling rig
Iceland Deep Drilling Project (IDDP) is quite noticeable in obtaining underground energy directly through drilling. Iceland is a country with many volcanoes. In the center of the volcano, a high-temperature heat source is developed for steam or water to generate electricity and provide local heat. In these areas, a well with a depth of 2000 ~ 3000 meters can generate 500 ~ 2000 kilowatts with a bottom temperature of 300℃ and a wellhead temperature of 200℃. Since 2002, preparations for drilling to a depth of 4000 ~ 5000 meters to investigate geothermal resources have been going on. The goal of this work is to determine whether it is technically and economically feasible to extract energy and chemical liquid when the critical point of fresh water temperature and pressure (374. 15℃, 22. 12 MPa) is above. In August 2008, the first deep well will be drilled in the Crafra geothermal field in the northeast of Iceland. When the well reaches the predetermined depth, the bottom temperature will be as high as 400 ~ 600℃, and the power generated by steam is estimated to be 4 ~ 50W. If this prediction of IDDP is confirmed, it will lead to great progress in the economy of high-temperature geothermal resources in Iceland and other regions. The fund for the first deep well has been secured, and the drilling project is planned to be completed within 4-5 months, and the borehole circulation test will be carried out in 2009.
Second, China Cretaceous continental scientific drilling Song Keyi well (Beijing) drilling project.
Song Ke 1 Well is a national 973 plan project "Major geological events of Cretaceous surface system and greenhouse climate change". In order to obtain the physical property data of Cretaceous strata for geoscience research, it is an environmental science drilling project arranged in Songliao basin in northeast China. The project consists of south well and north well (also known as main well), with the well depths of 18 10 m and 19 10 m respectively, and the core recovery rate is required to be 90%. Among them, the south well can be converted into an oil production well after completion, which was built by Daqing Oilfield according to the oil drilling procedure; Beijing only collects rock samples, which are undertaken by the Institute of Exploration Technology of China Geological Survey, and organized by China Geo University and Henan Geology and Mineral Engineering Company. The requirement of continuous coring drilling in this well makes it different from ordinary oil drilling; The formation encountered in drilling is lake basin deposition, and the completion diameter is 156 mm, so it is necessary to install an in-well pressure control system at the wellhead, which is different from geological core drilling. Therefore, the equipment and technology of Beijing construction have their own characteristics.
1. Equipment and pipelines-2000m water source drilling equipment
Due to the requirements for safe drilling in Wainai with deep well and caliper, the diameter of the drill pipe used in this well should not be less than 73mm, but the drilling depth of nearly 2,000 m can not be reached by using this kind of drill pipe in the domestic core drilling rig, so 2000m water source drilling equipment is selected. Compared with oil rigs drilling the same well depth, it has the advantages of light weight, small volume, low power consumption, small floor space and low operation and maintenance costs. Lift the drill string on the elevator and screw out the rotary table of the drilling rig, which is simple in operation and compact in matching; The disadvantage is that the tubing strength is low, unlike oil drilling, which can be fed strongly; The rotation speed of drilling rig is low, and the penetration rate is low when drilling hard rock; The lifting height of drilling rig is limited, and the auxiliary time of tripping is long.
2. Elevated drilling platform-meets the installation requirements of well control equipment.
The drilling platform of the 2000m water source drilling rig is directly located on the ground. In order to install the BOP at the wellhead, a steel foundation frame is designed, and the platform height is increased by 2. 1m (Figure 3). At the end of drilling, the frame bears the static load of 200 kn equipment, the drilling load of 400 kn hanging drill string and the gale load above level 7, and there is no sign of safety.
Fig. 3 Effect design of drilling rig underframe
3. Core drilling-core drilling technology
Specification and structure of drilling tools:
Outside diameter of drill bit:156mm.
Core diameter of common double-pipe drilling tool: 96 mm.
Core diameter of fidelity drilling tool (triple pipe): 82mm.
Maximum core clamping length: 9m.
The tail pipe of fidelity drilling tool is PC organic material pipe, which has good transparency, good rigidity and stable chemical properties. It is used to protect loose samples from interference during drilling, and the samples can be extracted with the pipe during coring without damage. Samples are easy to store and transport, and can be cut and studied after being frozen in test tubes.
(1) Liquid-tight sampling of quicksand layer: 162 ~ 2 1 1 m depth is unconsolidated quicksand layer, and the inner cavity of drilling tool must be completely isolated from flowing drilling fluid during drilling, otherwise the sand sample entering the bit will be partially or completely eroded and exhausted. The designed drilling tool was used to drill nearly 50m in the sand layer, and the sampling rate was 82% (Figure 4).
Fig. 4 Sampling effect of anti-liquid fidelity drilling tool
(2) Block alloy bit suitable for soft-medium hard stratum: the interval of 245-950m is a long section of soft mudstone and its interbedding with brittle or dense mudstone and sandstone. If the conventional bit structure is adopted, it is easy to drill in soft mudstone and the ROP is low in dense stratum. In addition, due to the poor collapse resistance and wear resistance of alloy tools, they need to be replaced frequently, and the rigid body of the drill bit is expensive. If the tools are replaced directly on the rigid body, the life of the rigid body will be short and the cost will increase. The embedded structure with large drainage and chip removal space shown in fig. 5a not only eliminates the phenomenon of mud drilling in soft mudstone, but also adapts to the change of soft and hard strata. 900-meter footage, rigid drilling 190 times, and pure drilling for nearly 700 hours, five bits can still be used. The rock stratum encountered by the drill bit is shown in fig. 5b.
(3) Rotary excavation combined with screw drilling is adopted in dense mudstone: after the well depth is 1250m, the stratum enters black dense mudstone. Whether alloy bit or PDC bit, the WOB is improved to 45kN, and the pumping capacity is 950L/min, but the ROP is only 0.2 ~ 0.3m/h, and the ROP is only about 0.5m/h with the turntable impregnated with diamond bit. The impregnated drill bit depends on the high-speed grinding of broken rocks, but due to the equipment Wainai, the maximum rotation speed of the turntable is only allowed to be 90 rpm during operation. In order to improve the bit speed and ROP, the screw motor is started to drive the bottom hole, and at the same time, the rotary table is started at a low speed (37 rpm) to eliminate the static friction between the drill string and the borehole wall, so as to evenly transmit WOB. The drilling effect of this measure can be compared from the following table.
Fig. 5 Inlaid alloy bit and its drilling effect
The development trend of contemporary earth science: the focus of the 33rd International Geological Congress
(4) Hydraulic coring device: The core of conventional drilling tools needs to be taken out directly from the inner tube. For large diameter drilling tools, the traditional coring method not only has high labor intensity and long coring time, but also causes plastic brittle core deformation and brittle core damage due to pipe plugging, mechanical vibration and free fall of core, and the original formation information is artificially destroyed. The hydraulic coring device developed in this well only needs to connect the slurry feeding pipe to the drilling tool, then seal the annular gap at the lower ends of the inner and outer pipes, and push the core out of the inner pipe by water pressure, which saves all links of the traditional coring method and truly realizes the nondestructive coring of the core of the conventional drilling tool. The principle and field work of the device are shown in Figure 5.
(5) Achievements of mud wall protection: The first spudding stratum is loose quicksand layer and soft mudstone, and the mud technology is not up to standard, which may easily lead to downhole accidents such as sticking and burying, and may also lead to drilling abandonment due to the collapse of long intervals. Trip 1 10 times in quicksand layer and soft mudstone layer for 53 calendar days from the first trip to the end of drilling, which not only never caused danger in the well, but also had regular well diameter and small settlement. During cementing, fluid injection in the well shows that the over-diameter coefficient of the well is less than 1.08. The total length of the second spudding interval is1.566m, the upper part is soft water-sensitive mudstone with brittle sandstone and conglomerate, and 850 ~1.500m contains multiple sections of easily falling strata. From the second spudding to the end of drilling in open hole 193 calendar days, the drilling tools were lifted for 295 times. There is no sticking accident caused by expansion and contraction of water-sensitive formation and falling off of brittle formation.
4. Comprehensive review
(1) Technical indicators of coring drilling (see table on next page).
(2) Technical and economic comparison between South and North wells: The North well used water drilling equipment and core drilling technology, which lasted for 8 months, the drilling depth was181m, the coring footage was 1630 m, and the core recovery rate was 95%; The south well used oil drilling equipment and technology, which lasted for 3 months. Drilling depth1915m, coring footage of 965m and core recovery rate of 98%. Compared with the objective conditions of the two wells, although coring in Beijing is difficult, the stratum encountered is complex, including 50m loose quicksand layer and 500m extremely dense mudstone. When the constructor enters the site, he knows nothing about the stratum properties. Generally speaking, the core recovery rate of the two methods can meet the requirements of scientific research. The drilling efficiency of oil drilling equipment is much higher than that of water drilling equipment; The engineering cost of oil drilling equipment is more than three times that of water drilling equipment. Therefore, under the premise that the project schedule meets the scientific research schedule, it is a feasible way to effectively reduce the scientific research cost by choosing the combination drilling technology to implement the environmental science drilling project.
The development trend of contemporary earth science: the focus of the 33rd International Geological Congress
(Author Zhu Yongyi)