Ultra-deep Reservoirs Research Articles

A fracture modeling method for ultra-deep reservoirs based on geologic information fusion: an application to a low porosity sandstone reservoirs in X gas field of a basin in western China

The reservoirs of ultra-deep and low-permeability sandstones typically exhibit characteristics of lithological tightness and poor physical properties. Fractures control the oil and gas content as well as the productivity of such reservoirs. However, the distribution of fractures is complex, exhibiting strong heterogeneity. Therefore, a systematic study on reservoir fracture modeling can provide geological foundations for the development of such reservoirs. Due to the considerable burial depth of these reservoirs, conventional methods relying solely on seismic information have limited reliability, and the established discrete network models of fractures are often less dependable. In this paper, taking the X gas reservoir in a basin in western China as an example, we discuss a fracture modeling method based on the integration of geological information to enhance the efficiency and accuracy of fracture modeling. The modeling method primarily involves the use of deterministic methods to obtain large-scale fractures, while random simulation is employed for small and medium-scale fractures. The fracture development control factors and seismic attribute information are integrated using permanence of ratios (PR) model to establish a fracture development probability field model. Subsequently, the geometric parameters of fractures and the fracture density model are used as input parameters to generate a discrete network model of small and medium-scale fractures using a object-based modeling method. Finally, based on the fracture equivalent property model and verified through geological understanding, analysis of production dynamics, and numerical simulation of the gas reservoir, it is demonstrated that the fracture model established using the proposed method aligns with geological understanding and exhibits high reliability.

Origin of gas condensate reservoir in Fuman Oilfield, Tarim Basin, NW China

To understand the reservoir property and hydrocarbon accumulation conditions of the Middle and Upper Ordovician intraplatform shoal between ultra-deep main strike-slip faults in Fuman Oilfield of the Tarim Basin, China, the main strike-slip faults in and around well FD1 in the basin were analyzed in terms of sedimentary facies, sequence stratigraphy, intraplatform shoal reservoir property, and oil and gas origins, based on drilling data. The Yingshan Formation intraplatform shoal between the main strike-slip faults is superimposed with low-order faults to form a new type of hydrocarbon play. Firstly, hydrocarbons generated from the Lower Cambrian Yuertusi Formation source rocks vertically migrated into the second member of Yingshan Formation through the main strike-slip faults, and then migrated laterally until they were accumulated. A small amount of oil from Well FD1 came from the Yuertusi Formation source rocks in the mature stage, and a large amount of gas originated from oil cracking in the ultra-deep reservoirs. Therefore, the secondary gas condensate reservoir in Well FD1 is characterized by high gas to oil ratio, dry gas (dryness coefficient being 0.970) and hybrid origin. This new type of hydrocarbon play characterized by intraplatform shoal and low-order fault suggests a prospect of continuous hydrocarbon-bearing area in Fuman Oilfield, which will expand the ultrap-deep oil and gas exploration in the oilfield.

Occurrence of deep liquid oil reservoirs in the Sichuan and Tarim basins as constrained by geological evidences and molecular simulation

The hydrocarbon phase state of deep to ultra-deep reservoirs in the Tarim and Sichuan basins has been of great interest in oil and gas exploration. Based on a combination of molecular dynamics simulation, gold-tube pyrolysis experiments, and geological-geochemical theory, this study discusses the mechanisms governing the stability of oils in deep reservoirs from the perspectives of their reservoir accumulation histories and chemical reactions. Generally, the reason for the existence of liquid oil in the Tarim Basin is widely considered to be only controlled by external geological conditions, mainly including low geothermal gradient, absence of thermal events, low maximum reservoir temperatures, and late hydrocarbon generation process. However, this study firstly proposed that the chemical composition of oil is an internal factor for its thermal stability. The simulation results reveal that the polycondensation reactions of asphaltene will release hydrogen atoms, which can provide a necessary hydrogen source for cracking of liquid chain hydrocarbons. It means that the presence of asphaltene components can promote the cracking of chain hydrocarbons and generate methane. The normal mature oil in the Sichuan Basin generally has higher contents of asphaltenes than that of the high-mature light oil of the Tarim Basin, so more hydrogen has historically been available for the cracking of oil to gas. By looking at the accumulation histories and chemical compositions of the crude oils, this study first explains the stable long-term storage of liquid hydrocarbons in the Tarim Basin, providing important guidance for future deep to ultra-deep oil and gas exploration.

Natural fractures in ultra-deep reservoirs of China: A review

In recent years, China has made significant progress in exploring oil and gas in sandstone and carbonate rocks with burial depths of more than 6000 m in the Tarim, Sichuan, and Junggar Basins. These ultra-deep reservoirs have widely developed natural fractures that are important storage spaces and primary flow pathways influencing hydrocarbon enrichment and production. For ultra-deep tight sandstone, fractures caused by tectonic, diagenetic, tectonic-diagenetic, and overpressure processes are widespread. In the foreland thrust belt, which is divided into five fracture domains, fault-related folds affect fracture distribution in ultra-deep sandstones. For ultra-deep carbonate rocks, strike-slip faults control scale, structural style, and linkage evolution of fractures. Fractures formed over multiple periods. Many fractures in Cretaceous sandstones formed recently whereas some of those in carbonate rocks formed in the Paleozoic when strata were buried less than 5000 m. With the increase in burial depth, fracture porosity (and, probably) connectivity is reduced by mineral deposits. Fracture-forming processes include overpressure, present in situ burial and tectonic loading. Other variables modifying fractures include when fractures formed (timing), regional and local structural position, and scale and fluid flow leading to heterogeneity in whether fractures are mineral filled, open, or enhanced by dissolution. Our review provides insights into the origins, characteristics, evolution, and effectiveness of fractures in ultra-deep sandstone and carbonate rocks.

Anisotropic mechanical behavior of ultra-deep shale under high in-situ stress, a case study in the Luzhou block of the southern Sichuan Basin, China

The safe and efficient development of ultra-deep shale gas deeper than 4500 m is closely related to the comprehensive evaluation of the mechanical behavior, brittleness and anisotropy characteristics of reservoir rocks under in-situ stress conditions. However, the above-mentioned information about ultra-deep shale is rarely reported. This study aims to fill this gap by systematically investigating the mechanical and anisotropic characteristics of cores, with 0° and 90° bedding orientations, from different layers in the vertical depth of 4900–4930 m, under confining pressure of 110 MPa. Furthermore, a new brittleness index with three parts related to brittle failure, i.e., the energy storage performance in the pre-peak stage, the performance of elastic energy used to maintain the post-peak failure, and the severity of the energy released during the post-peak stage, all of which are physically meaningful, was proposed. Subsequently, the index was validated and applied to the brittleness evaluation of ultra-deep reservoir rocks. The brittleness was evaluated in the following descending order: black shale of Longmaxi Formation ＞ gray-black shale of Wufeng Formation ＞ limestone of Baota Formation. Overall, the Wufeng- Longmaxi Formation shale still exhibits brittle failure under such high confining pressure, while the Baota Formation limestone exhibits quasi-ductile failure, which is consistent with the phenomenological behavior of cores. Further, various experimental techniques have been employed to study the brittle and quasi-ductile failure mechanisms of reservoir rocks. The anisotropy evaluation results show that the anisotropy degree of the mechanical and brittleness parameters corresponding to the deep formation is significantly lower than that of the shallow formation. The anisotropy degree of strength and deformation parameters (Young's modulus, Poisson's ratio) is closely related to the content of quartz and clay minerals, respectively. The above results are expected to provide data support and theoretical guidance for the development of deep and ultra-deep shale gas in the southern Sichuan region of China.

An Overview of the Differential Carbonate Reservoir Characteristic and Exploitation Challenge in the Tarim Basin (NW China)

The largest marine carbonate oilfield and gas condensate field in China have been found in the Ordovician limestones in the central Tarim Basin. They are defined as large “layered” reef-shoal and karstic reservoirs. However, low and/or unstable oil/gas production has been a big challenge for effective exploitation in ultra-deep (>6000 m) reservoirs for more than 20 years. Together with the static and dynamic reservoir data, we have a review of the unconventional characteristics of the oil/gas fields in that: (1) the large area tight matrix reservoir (porosity less than 5%, permeability less than 0.2 mD) superimposed with localized fracture-cave reservoir (porosity > 5%, permeability > 2 mD); (2) complicated fluid distribution and unstable production without uniform oil/gas/water interface in an oil/gas field; (3) about 30% wells in fractured reservoirs support more than 80% production; (4) high production decline rate is over 20% per year with low recovery ratio. These data suggest that the “sweet spot” of the fractured reservoir rather than the matrix reservoir is the major drilling target for ultra-deep reservoir development. In the ultra-deep pre-Mesozoic reservoirs, further advances in horizontal drilling and large multiple fracturing techniques are needed for the economic exploitation of the matrix reservoirs, and seismic quantitative descriptions and horizontal drilling techniques across the fault zones are needed for oil/gas efficient development from the deeply fractured reservoirs.

Multi-level ultra-deep fault-controlled karst reservoirs characterization methods for the Shunbei field

Ultra-deep carbonate fault-controlled reservoirs are characterized by large burial depths, low dissolution degrees, strong heterogeneity, and limited effective well data. Accurate 3D characterization based on seismic data is essential for efficient development of this type of reservoir. However, traditional seismic prediction methods are insufficient to accurately characterize different reservoir levels in the exploration and development of fault-controlled ultra-deep reservoirs. We propose a set of improved multi-level characterization methods for fault-controlled reservoirs. The improved methods could recover seismic information obscured by strong reflections and reduce the uncertainty of seismic interpretation. This study combined seismic strong reflection suppression and sedimentary strata seismic reflection interference elimination, proposed improved inversion methods, and advanced attribute calculation methods to improve the identification accuracy of reservoirs. In particular, we proposed the karst cave carving method based on improved inversion method and karst cave enhancement algorithm, the dissolved pore zone identification method based on optimization energy envelope algorithm, and the fault-fracture zone characterization method based on optimized atomic decomposition texture contrast. These methods were thoroughly validated by theoretical 3D models and field data. The proposed multi-level characterization methods can effectively improve the identification accuracy of fault-controlled karst reservoirs, provide a benchmark for predicting similar strong heterogeneous carbonate reservoirs, and provide reliable support for further facies modeling.

Seismic spatially variant noise suppression method in the Tarim Basin based on FFDNet and transfer learning

Due to a complex geologic structure and ultradeep reservoir location, noise distribution of prestack seismic data in the Tarim Basin is nonuniform. However, most of the current seismic random noise suppression methods lack the flexibility to deal with spatially variant random noise. To address this issue, we have developed an intelligent denoising method for seismic spatially variant random noise and applied it in the Tarim Basin. On the basis of denoising convolutional neural network (DnCNN), we add an extra channel to the input and introduce a tunable noise level map as input. The noise level map has the same dimensions as the input noisy seismic data, and each element in the noise level map corresponds to a denoising level. By adjusting the noise level map, a single model can handle noise with different levels as well as spatially variant noise. Due to the lack of labeled field data in the Tarim Basin, we introduce a transfer learning scheme that transfers features of effective signals learned from synthetic data to the denoiser for field data. The network learns the general and invariant features of an effective signal from a large number of easily obtained synthetic data and then learns the real effective signal characteristics from a small amount of approximately clean field data in the target area by fine-tuning. The processing results of synthetic and field data demonstrate that, compared with f- x deconvolution, dictionary learning, and DnCNN, our method exhibits high effectiveness in suppressing spatially variant random noise and preserves effective signals better.

Coupled relationships between overburden stress and ultra-deep sandstone brittle deformation properties based on in situ CT scanning

For low poroisty (tight) sandstone of the Cretaceous Bashijiqike Formation, Kuqa Depression foreland thrust belt (Tarim Basin), samples from an ultra-deep setting (ca.7–8 km depth) and from outcrop locations were collected to analyze and compare brittle deformation in triaxial tests to infer mechanical behavior. Core samples sustained protracted burial whereas outcrop samples were deeply buried then experienced late uplift and exposure. Fracture-pore changes during loading in situ uniaxial compression documented with 3D X-ray imaging show that loading results in extensive development of fractures and enhanced pore connectivity that elevates permeability from 1mD to 10mD through local tensile fracture zones and high-permeability layers. The collapse of 60% pores and 70% reduction of connected pores may lead to locally compacted low-permeability zones. These characteristics are also reflected in the high heterogeneity of ultra-deep reservoir properties—the alternating development of dense and sparse zones of fractures. Research lead to the inference that under burial and tectonic loading conditions sandstones experience concurrent collapse of pores and growth of fractures, and reservoir structure changes from pore-dominated to fracture-dominated. Under deep conditions, the reservoir rock is subjected to plastic-brittle strain, increasing porosity and permeability followed by, under ultra-deep conditions, porosity decreasing markedly and permeability increasing significantly.

Geochemistry of syntaxial calcite veins in ultra-deep sandstone reservoirs from the Kuqa depression, western China

Extensional fractures filled with calcite are widespread in the ultra-deep reservoir sandstones of the Cretaceous Bashijiqike Formation (>6000 m) in the Kuqa Depression, western China. Microstructures of calcite veins provide an excellent opportunity for investigating fracture opening processes in a tectonically active, ultra-deep foreland basin setting. The syntaxial calcite vein is the dominant type and is formed through a single crack-seal event. Calcite crystals in fractures show blocky and elongated blocky shapes. The textural and geochemical characteristics of syntaxial calcite veins were investigated in detail using optical cathodoluminescence, trace element distributions and stable carbon and oxygen isotopes. Calcite veins were inferred to have precipitated from a mixture of seawater and meteoric water. ∑REE + Y and elemental concentrations of Mg2+, Mn2+, Fe2+ and Sr2+ both increase from fracture walls to the center. This process was controlled by temperature, crystal growth rate and variations in elemental concentration in a relatively closed environment. Medium REE-bulge patterns after Post Archean Average Shale (PAAS) normalization, negative δCe and positive δEu anomalies all indicate that calcite wall-rock cements and veins may inherit constituents from seawater and from meteoric water containing feldspar-weathering components, respectively. Both 13δCPDB and 18δOSMOW of the parent fluids imply that calcite veins were primarily precipitated from seawater under a relatively closed diagenetic environment. Considering the scope and timing of the transgression of the Tethyan Ocean in the study area, meteoric water may have been retained prior to the seawater invasion (65 Ma). The mixing of meteoric water and seawater within the reservoir could be the primary origin of the fluids forming the calcite veins.

Origin of breccia dolomites in the middle Devonian Guanwushan Formation, NW Sichuan Basin, China: Implications for ultra-deep carbonate reservoirs

Deep to ultra-deep carbonate rocks have become a target for hydrocarbon exploration. The formation mechanisms of these deep to ultra-deep reservoirs are very complicated, and no consensus has yet emerged. This paper reports an investigation into the Middle Devonian Guanwushan Formation in the NW Sichuan Basin, China, which is a typical ultra-deep dolomite reservoir. Drilling-core and thin-section observations identified breccia matrix dolomite (MD) and interbreccia-filling dolomite (FD), of which the FD is commonly associated with sphalerite and barite. Geochemical analyses, including C and O isotopes, trace and rare earth element (REE) contents, and fluid inclusions, were conducted to investigate the origins of the different types of dolomite. Results indicate that the MDs generally retain the signature of syn-depositional seawater (relatively positive δ18O, low Fe and Mn, left-leaning REE patterns, and negative Ce anomalies), with involvement of meteoric water (relatively high Al, Ti and ΣREE). In contrast, the FDs were the diagenetic product of deep hydrothermal fluids (depleted δ18O, high Fe and Mn, and enrichment in MREEs), and the homogenization temperature of fluid inclusions is much higher than the normal burial geothermal temperature. The breccia dolomite reservoirs of the Guanwushan Formation were deposited as reef-core micro-facies and formed during the depositional to early diagenetic stages, and were the result of subaerial seawater dolomitization and meteoric water karstification. However, hydrothermal fluids subsequently modified the reservoir by cementation and filling. The Guanwushan Formation is a typical case of an ultra-deep carbonate reservoir that formed during the depositional to early diagenetic stages but was filled at the burial stage. Therefore, the favorable reservoir zones associated with deposition and early diagenesis should be the targets of future exploration. The findings of this study are expected to be of general significance for deep and ultra-deep oil and gas exploration in other regions and countries.

Study on the influence of temperature on fracture propagation in ultra-deep shale formation

Creating a complex fracture network by hydraulic fracturing was an essential technic for the development of ultra-deep reservoirs. Due to the effect of thermal stress field on fracture propagation was unclear, it was necessary to understand the interaction mechanism between hydraulic fracture and bedding plane in layered formation. Combined with the experiments, the numerical simulation model was proposed based on the damage mechanics theory to illustrate the fracture propagation mechanism under high temperature. The simulations indicated that the reservoir temperature was a predominant factor affecting the fracture propagation when the temperature was over 200 ℃. Under high reservoir temperature, the breakdown pressure and extension pressure reduced by 7.61 % and 8.44 % compared with the reservoir temperature was 25 ℃, and the average fracture width increased by 23 %. Combined with the triaxial rock mechanics test and CT scanning, it indicated that the increased temperature difference between reservoir and fracturing fluid contributed the degradation mechanism of rock mechanical properties, the main reason was that the higher temperature difference induced the growth of micro fracture system in the reservoir, making the opening of micro fracture larger and the number of micro fracture increased, so the mechanical strength of rock experienced a dramatically decrease. With the degradation mechanism of rock mechanical properties, the mechanical strength difference between rock and bedding plane was reduced, thus the hydraulic fracture was more easily cross the bedding plane.

Quantitative prediction of multistage fractures of ultra-deep tight sandstone based on the theory of minimum energy dissipation

Due to strong reservoir heterogeneity and low-resolution limit of geophysical data, it is difficult to predict fractures in ultra-deep reservoirs by conventional methods. In this research, we established a novel geomechanical model for prediction of fracture distribution in brittle reservoirs, especially for ultra-deep tight sandstone reservoirs. Methodologically, we intended to introduce the minimum energy dissipation principle considering time variable, combined with the generalized Hooke’s law containing damage variable, and obtained the energy dissipation rate expression corresponding to the energy dissipation process of brittle rocks. Combined with the three-shear energy yield criterion, the Lagrangian multiplier was introduced to deduce and construct the constitutive model and the failure criterion of rocks under the framework of the theory of minimum energy dissipation. Based on the law of conservation of energy, the stress-energy coupling characterization model of fracture density parameter was derived. Finally, all the improved geomechanical equations were incorporated into a finite element software to quantitatively simulate the distributions of tectonic stress filed and fractures based on paleo-structure restoration of Keshen anticline during the middle and late Himalayan periods. Its predictions agreed well with measured fracture density from reservoir cores and image logs.

Tectonic Factors Restricting Differences among Layers in Microstructure of Ultradeep Clastic Rock Reservoir: A Case Study on Cretaceous Bashijiqike Formation in Kuqa Depression

Abstract The Cretaceous Bashijiqike Formation in the Kelasu structural belt of Kuqa Depression is an ultradeep reservoir with burial depth of more than 6 km. Due to the influence of strong thrust nappe from the South Tianshan in the north, the burial depth gradually deepened from north to south in the Kelasu tectonic belt. With the increase of the burial depth, the influence of tectonic compression relatively weakens, and the formation mechanism that affects the microstructure of ultradeep clastic reservoir is changed. Comprehensive analysis of thin section and quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN), scanning electron microscope (SEM), and micro-CT scanning are used to investigate the characteristics of the Cretaceous Bashijiqike Formation at the depth of 8000 m (TVD) in various stress sections. The result shows that, for the ultradeep reservoir with burial depth up to 8000 m, its reservoir characteristics and interlayer differences are not completely restricted by the neutral surface effect. (1) The porosity and permeability of various stress sections are different, and the reservoir physical properties of the tensile section are higher than that in the compressive section. (2) The pore types, pore radius, and pore throat connectivity of various stress sections are different, and the development of pores and throats in the tensile section is better than that in the compressive section. (3) As an ultradeep clastic rock reservoir, the vertical fracture development characteristics of Well Bozi9 at the depth of 8000 m differ from that in Kela-Keshen area at the depth of 6000 m in the model of strain neutral surface. The interlayer difference in the microstructure of ultradeep clastic rock reservoir is clarified, which has a positive effect to evaluate and predict the distribution of favorable deep reservoir.

Experimental Study on Gas Injection for Ultra Deep and high-pressure Fractured-vuggy Carbonate Oil Reservoirs

Experimental Study on Gas Injection for Ultra Deep and high-pressure Fractured-vuggy Carbonate Oil Reservoirs

Comparison between L2- and L1-norm and among optimization algorithms for a nonhyperbolic multiparametric approach for converted-wave and OBN data

As velocity analysis is an important step in seismic processing, several nonhyperbolic travel-time approximations have been proposed during the last decades, and each nonhyperbolic approximation was developed for different conditions and with different proposals. However, none of them was proposed to consider the combined effect of the nonhyperbolicity coming from layered media with large offsets, wave conversion and difference of datum between source and receiver. For this, a nonhyperbolic multiparametric travel-time approximation, which is capable of describing this combination of effects, was recently proposed. As this approximation was developed to characterize ultra-deep reservoirs, the understanding of its behavior is necessary for an offshore reservoir concerning the objective function topology complexity, as it is important for a better understanding of its behavior during the inversion procedure, and also important to determine the kind of optimization algorithm to be used. Performing the inversion procedure with different optimization algorithms and norms is proposed. The complexity analysis of the objective function is also proposed. Then, a comparison between each norm and among each algorithm concerning their accuracy and efficiency is proposed, to find which combination is the most effective to recover RMS velocity information for this kind of scenario.

3D natural fracture model of shale reservoir based on petrophysical characterization

The existence and distribution of natural fractures in shale reservoirs is of great significance to shale gas exploitation. A 3D fracture spatial distribution model with varying reservoir burial depth and regional tectonicsin southeastern Chongqing is constructed based on an enhanced DFN modeling method. Fracture volume density (P32) is calculated by petrophysical test and verified from test wells. The geometric parameters of fractures (length, occurrence, opening) are clustered by regional tectonics. Uncertainties are considered by a stochastic description of the fracture network geometry, utilizing Monte Carlo simulation techniques. The application of the model in seven wells and the quantitative analysis of the relationship between fracture density and burial depth allow the modeling to be extended to deep and ultra-deep reservoirs. Fracture models with reservoirs buried depth over 3000 m are predicted and analyzed. For the various input parameters, the influence of model size and fracture shape on model reliability is analyzed. The establishment of fracture model can effectively quantitatively characterize the reservoir fracture distribution at different burial depths, and its efficient implementation in finite element software can provide support for shale gas mining engineering.

Modified Laponite synthesized with special wettability as a multifunctional additive in oil-based drilling fluids

In this study, Modified Laponite with lyophobic wettability was synthesized as a multi-functional additive to solve instability of emulsions, rheological deterioration, and wellbore instability of oil-based drilling fluid. Properties and its influence on emulsion stability, rheological behavior and plugging property were investigated. The results showed that Modified Laponite was in a shape of sheet layer and had micro-meter length and nano-meter thickness which was in match with the diameter of shale pores. And it was proved to be resistant to approximately 450 °C by thermogravimetric analysis measurement. Mechanism analysis revealed that Modified Laponite could stable the oil-based drilling fluid through four sections. Firstly, Modified Laponite with lyophobic wettability could promote its existence in the interface of brine/mineral oil. Secondly, Modified Laponite could decrease the interfacial tension from 32.8 to 13.5 mN/m to maintain the emulsion particles in a small size for a long time then to ensure the emulsion stability. Thirdly, Modified Laponite could enhance the shear-thinning rheological behavior which could maintain the rheological stability and enhance the sedimentation stability in ultra-deep reservoirs with high temperature and high pressure conditions. Fourthly, Modified Laponite could plug the shale pores effectively by preventing pressure transmission and enhancing shale compressive strength, and decrease the filtration volume of oil-based drilling fluid from 7.4 mL to 2.6 mL after aging at 180 °C for 16 h to stable the wellbore. Therefore, Modified Laponite was a multifunctional additive to stable the emulsion, enhance the rheological stability and strength the wellbore stability, which could ensure the application of oil-based drilling fluid in drilling process of ultra-deep reservoirs.

In situ measurement equipment for the elastic wave velocity of rocks under various temperature and pressure conditions of ultra-deep reservoirs.

A novel equipment for measuring the elastic wave velocity of rocks under various temperature and pressure conditions of ultra-deep reservoirs has been developed. The equipment consists of a high pressure and high temperature experimental platform and an ultrasonic measurement system, which can measure the elastic wave velocity of rocks under conditions of ultra-deep reservoirs up to a depth of 13 km by the ultrasonic reflection method. The method of assembling rock samples has also been improved to acquire high-quality ultrasonic signals. The feasibility of the new equipment was tested by measuring the elastic wave velocity of dolomite and limestone. The experimental results are consistent with the previous research. The elastic wave velocity of rocks measured by this equipment can be potentially used for the exploration of ultra-deep oil and gas resources.

Drilling speed-up and production-increasing development practice of ultra deep clastic reservoir based on Geology-Engineering integration in the Tarim Basin, Northwest China

Kelasu structural belt in Tarim Basin has a large reservoir burial depth and complex geological conditions, and challenges such as ultra-deep, high temperature, high pressure, and high stress lead to big problems related to well control safety and project quality. To solve these key technical problems that set barriers to the process of exploration and development, a set of drilling technology processes via geology-engineering integration is established with geomechanics as the bridge. And an integrated key drilling engineering technology for the safe speed-up of ultra-deep wells was formed, integrating well location optimization, well trajectory optimization, stratum pressure prediction before drilling, stratum drillability evaluation, and bit and speed-up tool design and optimization. Combined with seismic data, logging data, structural characteristics, and lithology distribution characteristics, the rock mechanics data volume related to the three-dimensional drilling resistance characteristics of the block was established for the first time, and the vertical and horizontal heterogeneity was quantitatively characterized, which provided a basis for bit design, improvement, and optimization. During the process of drilling, the geomechanical model shall be corrected in time according to the actual drilling information, and the drilling “three pressures” data shall be updated in real-time to support the dynamic adjustment of drilling parameters. Through field practice, the average drilling complexity rate was reduced from 18% to 4.6%, and the drilling cycle at 8500 m depth was reduced from 326 days to 257 days, which were significantly better than those of the vertical wells deployed in the early stage without considering geology-engineering integration.