Research progress and development of deep and ultra-deep drilling fluid technology

The research progress of deep and ultra-deep drilling fluid technology systematically reviewed,the key problems existing are analyzed,and the future development direction is proposed.In view of the high temperature,high pressure and high stress,fracture development,wellbore instability,drilling fluid lost circulation and other problems faced in the process of deep and ultra-deep complex oil and gas drilling,scholars have developed deep and ultra-deep high-temperature and high-salt resistant water-based drilling fluid technology,high-temperature resistant oil-based/synthetic drilling fluid technology,drilling fluid technology for reservoir protection and drilling fluid lost circulation control technology.However,there are still some key problems such as insufficient resistance to high temperature,high pressure and high stress,wellbore instability and serious lost circulation.Therefore,the development direction of deep and ultra-deep drilling fluid technology in the future is proposed:(1)The technology of high-temperature and high-salt resistant water-based drilling fluid should focus on improving high temperature stability,improving rheological properties,strengthening filtration control and improving compatibility with formation.(2)The technology of oil-based/synthetic drilling fluid resistant to high temperature should further study in the aspects of easily degradable environmental protection additives with low toxicity such as high temperature stabilizer,rheological regulator and related supporting technologies.(3)The drilling fluid technology for reservoir protection should be devoted to the development of new high-performance additives and materials,and further improve the real-time monitoring technology by introducing advanced sensor networks and artificial intelligence algorithms.(4)The lost circulation control of drilling fluid should pay more attention to the integration and application of intelligent technology,the research and application of high-performance plugging materials,the exploration of diversified plugging techniques and methods,and the improvement of environmental protection and production safety awareness.

Hydrophobic silica nanoparticle-stabilized invert emulsion as drilling fluid for deep drilling

An oil-based drilling fluid should be stable and tolerant to high temperatures for use in deep drilling. An invert emulsion of water in oil is a good choice as an oil- based drilling fluid which is a mixture of a solid phase and two immiscible liquid phases stabilized by a polymeric surfactant. In deep drilling, due to high temperatures, the polymeric surfactant degrades and a phase separation occurs. Here, octadecyltrimethoxysilane-modified silica nanoparticles were used to form a stable invert emulsion of water in oil for the drilling fluid model which resulted in a milky fluid with the formation of 60 gm water droplets. In addition, rheological study showed that using hydrophobic silica nanoparticles resulted in a stable water in oil invert emulsion with desired properties for a drilling fluid that can be modified by adjusting the nanoparticle nature and content. Aging experiments at 120 ℃ indicated that they also have good stability at high temperatures for challenging drilling operations.

The accurate location of the injection- induced microearthquakes in German Continental Deep Drilling Program

From August 21, 2000 to October 20, 2000,a fluid injection-induced seismicity experiment has been carried out in the KTB (German Continental Deep Drilling Program). The KTB seismic network recorded more than 2 700 events. Among them 237 events were of high signal-to-noise ratio, and were processed and accurately located. When the events were located, non KTB events were weeded out by Wadatis method. The standard deviation, mean and median were obtained by Jackknife's technique, and finally the events were accurately located by Gei-gers method so that the mean error is about 0.1 km. No earthquakes with focal depth greater than 9.3 km, which is nearly at the bottom of the hole, were detected. One of the explanation is that at such depths the stress levels may not close to the rocks frictional strength so that failure could not be induced by the relatively small perturbation in pore pressure. Or at these depths there may be no permeable, well-oriented faults. This depth may be in close proximity to the bottom of the hole to the brittle-ductile transition, even in this relatively stable interior of the in-teraplate. This phenomenon is explained by the experimental results and geothermal data from the superdeep bore-hole.

Deep Drilling Campaign in the Western Qaidam Basin,NE Tibetan Plateau and their Revealed Global Temperature Forcing of Salt Formation in the Late Miocene-Quaternary

The Qaidam Basin in the NE Tibetan Plateau has contributed the largest amount of potash in China.However,how the potash was formed has long been a subject of debate.Here we carried out a deep drilling

Assessing the range of blasting-induced cracks in the surrounding rock of deeply buried tunnels based on the unified strength theory

Blasting-induced cracks in the rock surrounding deeply buried tunnels can result in water gushing and rock mass collapse,posing significant safety risks.However,previous theoretical studies on the range of blasting-induced cracks often ignore the impact of the in-situ stress,especially that of the intermediate principal stress.The particle displacement−crack radius relationship was established in this paper by utilizing the blasthole cavity expansion equation,and theoretical analytical formulas of the stress−displacement relationship and the crack radius were derived with unified strength theory to accurately assess the range of cracks in deep surrounding rock under a blasting load.Parameter analysis showed that the crushing zone size was positively correlated with in-situ stress,intermediate principal stress,and detonation pressure,whereas negatively correlated with Poisson ratio and decoupling coefficient.The dilatancy angle-crushing zone size relationship exhibited nonmonotonic behavior.The relationships in the crushing zone and the fracture zone exhibited opposite trends under the influence of only in-situ stress or intermediate principal stress.As the in-situ stress increased from 0 to 70 MPa,the rate of change in the crack range and the attenuation rate of the peak vibration velocity gradually slowed.

Deep scientific drilling results from Koyna and Killari earthquake regions reveal why Indian shield lithosphere is unusual, thin and warm

The nature of crustal and lithospheric mantle evolution of the Archean shields as well as their subsequent deformation due to recent plate motions and sustained intraplate geodynamic activity, has been a subject of considerable interest. In view of this, about three decades ago, a new idea was put forward suggesting that out of all shield terrains, the Indian shield has an extremely thin lithosphere（w100 km,compared to 250e350 km, elsewhere）, apart from being warm, non-rigid, sheared and deformed. As expected, it met with scepticism by heat flow and the emerging seismic tomographic study groups, who on the contrary suggested that the Indian shield has a cool crust, besides a coherent and thick lithosphere（as much as 300e400 km） like any other shield. However, recently obtained integrated geological and geophysical findings from deep scientific drillings in 1993 Killari（M w： 6.3） and 1967 Koyna（M w： 6.3）earthquake zones, as well as newly acquired geophysical data over other parts of Indian shield terrain,have provided a totally new insight to this debate. Beneath Killari, the basement was found consisting of high density, high velocity mid crustal amphibolite to granulite facies rocks due to exhumation of the deeper crustal layers and sustained granitic upper crustal erosion. Similar type of basement appears to be present in Koyna region too, which is characterized by considerably high upper crustal temperatures.Since, such type of crust is depleted in radiogenic elements, it resulted into lowering of heat flow at the surface, increase in heat flow contribution from the mantle, and upwarping of the lithosphereasthenosphere boundary. Consequently, the Indian shield lithosphere has become unusually thin and warm. This study highlights the need of an integrated geological, geochemical and geophysical approach in order to accurately determine deep crust-mantle thermal regime in continental areas.

A high-temperature resistant and high-density polymeric saturated brine-based drilling fluid

Three high-temperature resistant polymeric additives for water-based drilling fluids are designed and developed:weakly cross-linked zwitterionic polymer fluid loss reducer(WCZ),flexible polymer microsphere nano-plugging agent(FPM)and comb-structure polymeric lubricant(CSP).A high-temperature resistant and high-density polymeric saturated brine-based drilling fluid was developed for deep drilling.The WCZ has a good anti-polyelectrolyte effect and exhibits the API fluid loss less than 8 mL after aging in saturated salt environment at 200°C.The FPM can reduce the fluid loss by improving the quality of the mud cake and has a good plugging effect on nano-scale pores/fractures.The CSP,with a weight average molecular weight of 4804,has multiple polar adsorption sites and exhibits excellent lubricating performance under high temperature and high salt conditions.The developed drilling fluid system with a density of 2.0 g/cm^(3)has good rheological properties.It shows a fluid loss less than 15 mL at 200°C and high pressure,a sedimentation factor(SF)smaller than 0.52 after standing at high temperature for 5 d,and a rolling recovery of hydratable drill cuttings similar to oil-based drilling fluid.Besides,it has good plugging and lubricating performance.

Stability and nonlinear dynamic behavior of drilling shaft system in copper stave deep hole drilling

The stability and nonlinear dynamic behavior of drilling shaft system in copper stave deep hole drilling were analyzed. The effects of the fluctuation of the cutting force, the mass eccentricity and the hydrodynamic forces of cutting fluid could be taken into consideration in the model of drilling shaft system. Based on the isoparametric finite element method, the variational form of Reynolds equation in hydrodynamic fluid was used to calculate nonlinear hydrodynamic forces and their Jacobian matrices simultaneously. In the stability analysis, a new shooting method for rapidly determining the periodic orbit of the nonlinear drilling shaft system and its period was presented by rebuilding the traditional shooting method and changing the time scale. Through the combination of theories with experiment, the correctness and effectiveness of the above methods are verified by using the Floquet theory. The results show that the mass eccentricity can inhibit the whirling motion of drilling shaft to some extent.

Development and Performance Evaluation of a Deep Water Synthetic Based Drilling Fluid System

With the enhancement of environmental protection awareness, the requirements on drilling fluid are increasingly strict, and the use of ordinary oil-based drilling fluid has been strictly restricted. In order to solve the environmental protection and oil-gas reservoir protection problems of offshore oil drilling, a new synthetic basic drilling fluid system is developed. The basic formula is as follows: a basic fluid (80% Linear a-olefin + 20% Simulated seawater) + 2.5% nano organobentonite + 3.5% emulsifier RHJ-5# + 2.5% fluid loss agent SDJ-1 + 1.5% CaO + the right amount of oil wetting barite to adjust the density, and a multifunctional oil and gas formation protective agent YRZ has been developed. The performance was evaluated using a high-low-high-temperature rheometer, a high-temperature and high-pressure demulsification voltage tester, and a high-temperature and high-pressure dynamic fluid loss meter. The results show that the developed synthetic based drilling fluid has good rheological property, demulsification voltage ≥ 500 V, temperature resistance up to 160°C, high temperature and high pressure filtration loss < 3.5 mL. After adding 2% - 5% YRZ into the basic formula of synthetic based drilling fluid, the permeability recovery value exceeds 90% and the reservoir protection effect is excellent. The new synthetic deepwater drilling fluid is expected to have a good application prospect in offshore deepwater drilling.

Frequency Analysis of Drill Bit Whirlings on Uneven Bottoms of Deep Bore-holes

An incipient stage of a rotating drill string bit whirl motion proceeding on a well bottom surface is studied on the basis of kinematic （nonholonomic） models of mechanic interaction between the contacting uneven bodies. The bit is considered to be an absolutely rigid spherical or ellipsoidal body, the well bottom surface can be plane or spherical. It is assumed that the system coaxiality is disturbed through small initial curvature of the drill string, imperfections of the bit and bore-well geometry or the system mass debalance. Linearized equations of the bit whirling are deducted, the frequencies of periodic motions are calculated, and their modes are constructed for different geometric parameters of the spherical and ellipsoidal bits. It is demonstrated that, depending on the system properties, the bit motion can acquire the regimes of forward and backward whMings or to transit to the state of stationary spinning relative to an immovable center of velocities. The most unfavorable and atypical whirling modes are characteristic for oblate eilipsoidal bits and curvilinear surfaces of the well bottom.

New perspective of Miocene marine hydrocarbon source rocks in deep-water area in Qiongdongnan Basin of northern South China Sea

Drilling wells reveal that the organic matter abundance of Miocene marine source rocks in shallow water area of the Qiongdongnan Basin is relatively low with poor hydrocarbon generation poten- tial. However, in some drilling wells of deep water area close to the central depression belt, Miocene marine source rocks with better organic matter abundance and hydrocarbon generation have been found, which have achieved better source rock standard based on the analysis of geochemical charac- teristics. Although there are no exploratory wells in deep water area of the research region, through the comparative analysis of geochemical data of several typical exploratory wells respectively from shallow water area in the basin, central depression belt margin in deep-water area of the basin and Site 1148 of deep sea drilling in the South China Sea Basin, it reveals that the tendency of the quality of source rocks becomes positive gradually from delta to bathyal environment, which then becomes negative as in deep oceanic environment. Owing to the lack of terrestrial organic matter input, the important controlling factors of Miocene marine source rocks in the Qiongdongnan Basin are ocean productivity and preservation conditions of organic matter. The element geochemistry data indicate that the tendency of the paleoproductivity and the preservation conditions of organic matter become positive as water depth increase from shallow area to bathyal area close to central depression belt. So it is speculated that there must exist high quality source rocks in the central depression area where the preservation conditions of organic matter are much better. Besides, in theory, in oxygen-poor zone of oceanic environment at the water depth 400–1 000 m, the preservation conditions of organic matter are well thus forming high-quality marine source rocks. The result- ing speculation, it is reasonable to consider that there are high hydrocarbon generation potential source rocks in bathyal environment of the Qiongdongnan Basin, especially at the water depth 400– 1 000 m.

The biodiesel-based flat-rheology drilling fluid system

As the base oil of the current flat-rheology synthetic drilling fluid is high in cost and not renewable, the biodiesel-based flat-rheology drilling fluid with low-cost, environmental protection and renewable advantage was studied. Based on the optimization of raw materials, a cheap, environment-friendly biodiesel of soybean oil ethyl ester with good fluidity at low temperature was selected as the base oil. By selecting high oil-water ratio and introducing cationic surfactant into the auxiliary emulsifier, the thickening of biodiesel-based emulsion caused by hydrolysis and saponification after high-temperature aging was effectively eliminated. The organoclay prepared with cationic modifier of hexadecyl trimethyl ammonium chloride was used to improve the rheologic properties, stability and fluid loss of the drilling fluid while preventing low-temperature thickening. A flat-rheology modifier was synthesized with dimer fatty acid and cocoanut fatty acid diethanolamide, which could form strong network structure in the biodiesel-based drilling fluid to adjust effectively rheological properties of the drilling fluid. A biodiesel-based flat-rheology drilling fluid system with the density of 1.2 g/cm^(3) has been formulated which has constant rheology in the temperature range of 2-90 ℃, temperature tolerance of 160 ℃, seawater salinity tolerance of 5%, shale cuttings tolerance of 10%, and is environmentally friendly.

Critical Buckling of Drill Strings in Cylindrical Cavities of Inclined Bore-Holes

Notwithstanding the fact that the problem of drill string buckling （Eulerian instability） inside the cylindrical cavity of an inclined bore-hole attracts attention of many specialists, it is far from completion. This peculiarity can be explained by the complexity of its mathematic model which is described by singularly perturbed equations. Their solutions （eigen modes） have the shapes of boundary effects or buckles （harmonic wavelets） localized in zones of the bore-hole that are not specified in advance. Therefore, the problem should be stated in the domain of entire length of the drill string or in some separated part including an expected zone of its buckling. In the paper, a mathematic model for computer analysis of incipient buckling of a drill string in cylindrical channel of an inclined bore-hole is elaborated. The constitutive equation is deduced with allowance made for action of gravity, contact, and friction forces. Computer simulation of the drill string buckling is performed for different values of the bore-hole inclination angle, its length, friction coefficient, and clearance. The eigen values （critical loads） are found and modes of stability loss are constructed. The numerical results for the case when the inclination angle equals friction angle coincide with ones obtained analytically.

Mineralogical and Geochemical Evidence of Fluid-rock Interaction at the Shallow Crustal Level in Koyna Seismogenic Region, Maharashtra, India: Impact and Implications

The Koyna region of Maharashtra located in the western part of the~65 Myr old Deccan traps province,overlying the Neoarchean cratonic granitoid basement of peninsular India,has been experiencing recurring seismicity since 1962 after the impoundment of the Shivajisagar Reservoir behind the Koyna Dam.

Response of Surface Soft Soil and Fine-Grained Sand Layers to Seismic Waves

Shanghai is located in eastern China and is built on overburden soil layers. It can be seen from the Mexico M S=8.1 earthquake on September 19, 1985 and the Hanshin M S=7.4 earthquake on January 17,1995 that heavy casualties and property losses have a direct relationship with overburden soil layers. Ground motions caused by earthquakes are significantly amplified when passing through the soil layers. Under the influence of these amplified motions, building structures, whose nature frequency is within the frequency band of soil amplification response, will experience more severe damage than those built on bedrock. Therefore, engineering seismologists have paid considerable attention the amplification responses in the Shanghai overburden soil layers. The amplification responses of soil and sand layers in this paper are given by the M L=4.1 earthquake in Nantong, Jiangsu Province on December 25, 2001 at 31.8° N, 120.9° E. It can be seen that the responses of soil and sand layers are very different. That is important.

Experimental and computational analysis of the coolant distribution considering the viscosity of the cutting fluid during machining with helical deep hole drills

An experimental analysis regarding the distribution of the cutting fluid is very difficult due to the inaccessibility of the contact zone within the bore hole.Therefore,suitable simulation models are necessary to evaluate new tool designs and optimize drilling processes.In this paper the coolant distribution during helical deep hole drilling is analyzed with high-speed microscopy.Micro particles are added to the cutting fluid circuit bya developed high-pressure mixing vessel.After the evaluation of suitable particle size,particle concentration and coolant pressure,a computational fluid dynamics(CFD)simulation is validated with the experimental results.The comparison shows a very good model quality with a marginal difference for the flow velocity of 1.57%between simulation and experiment.The simulation considers the kinematic viscosity of the fluid.The results show that the fluid velocity in the chip flutes is low compared to the fluid velocity at the exit of the coolant channels of the tool and drops even further between theguidechamfers.Theflow velocity and the flow pressure directly at the cutting edge decrease to such an extent that the fluid cannot generate a sufficient cooling or lubrication.With the CFD simulation a deeper understanding of the behavior and interactions of the cutting fluid is achieved.Based on these results further research activities to improve the coolant supply can be carried out with great potential to evaluate new tool geometries and optimize the machining process.