Success Rate Of Drilling Research Articles

Success Rate of Drilling and Knuckle Wire Crossing Technique in Chronic total Occlusion of the Femoro-Popliteal Artery and Predicting Factors Related to it in Real-World Data

Objective: Crossing chronic total occlusion (CTO) in femoro-popliteal (FP) arteries is challenging. Hence, this study aimed to describe real-world data on the technical success rate of crossing FP CTO lesions, and analyze predicting factors for crossing failure. Material and Methods: This retrospective study, conducted at a single center, involved patients with peripheral arterial disease (PAD) and FP CTOs, categorized as Rutherford categories 3-6, having undergone endovascular recanalization from 2017 to 2022. Baseline characteristics and crossing success rates were described using frequencies, percentages, means, medians, standard deviations, and interquartile ranges. Factors associated with crossing failure were analyzed through logistic regression analysis, with statistical significance set at a p-value<0.05.Results: Among the 181 patients analyzed, the majority exhibited minor tissue loss (63%) and severe disease (TASC II category D, GLASS grade 4). The predominant CTO crossing approach was based on plaque cap morphology (CTOP) classification type B (66.9%), with severe CTO calcification (PACSS type 4) in 23.8%. Median occlusion length was 16.1 cm; 85.6% successfully crossed the CTO and antegrade success was 57.5%. Factors associated with crossing failure included: CTOP types C or D, CTO at the P3-popliteal artery, severe CTO calcification, and dyslipidemia. Retrograde recanalization showed higher success rates in CTOP type D and longer occlusions.Conclusion: This study highlights the safety and effectiveness of the catheter-wire crossing technique for FP CTOs. CTOP classification, CTO location, severe calcification, and dyslipidemia predicted crossing failure. The retrograde approach works well in CTOP type D and longer CTOs, providing insights for improving success in clinical practice.

Formation mechanism of deep to ultra-deep carbonate reservoir: a case study of the Ediacaran Dengying Formation, Penglai area, Sichuan Basin

The formation of high-quality deep to ultra-deep carbonate reservoirs presents a topic worthy of thorough exploration. Focusing on the Ediacaran (Sinian) Dengying Formation in the Penglai area of the Sichuan Basin, we analysed genesis mechanisms of deep to ultra-deep marine carbonate reservoirs through drilling/logging, seismic data and analytical tests, which showed the dolomite reservoir primarily consists of secondary solution pores and cavities, exhibiting characteristics of vertical overlap and horizontal continuous distribution. The microbial mound beach, which represents the main dominant facies type within the reservoir, can be categorised into three types: high-quality reservoir, medium-quality reservoir and poor reservoir. The reservoir has undergone five stages: syngenetic to quasi-syngenetic, shallow burial, supergene, burial and deep burial adjustment stages. It is postulated that the development of deep to ultra-deep carbonate reservoirs is governed by sedimentary facies, with the type and structure of carbonate influencing the development and evolution of reservoir pores. Multiphase diagenetic fluids further modify and enhanced the properties of the reservoirs. Deep and ultra-deep carbonate reservoirs exhibit strong heterogeneity, and high-quality reservoirs are characterised by multi-factor joint control and multi-stage composite genesis. The lithological and structural–lithological traps associated with them commonly cluster in large areas so effective identification of favourable sedimentary facies and reservoirs is crucial for predicting deep to ultra-deep carbonate reservoirs, characterising traps and improving the success rate of drilling.

Improved method for quantitative fault sealing evaluation in sand-clay sequences: A case study from the west subsag of Bozhong Sag in the Bohai Bay basin, China

This research aims to enhance the assessment of fault sealing capacity and predicting sealing hydrocarbon column height prior to drilling, which is instrumental in enhancing drilling success rates. Traditional methods for fault seal evaluation, which primarily consider the fault rock's clay content, often overlook the influence of effective fault normal stress (σNeff). This research analyzed numerous drilled fault-bounded reservoirs in the west subsag of Bozhong Sag to determine the fault sealing's buoyancy pressure (Pb). The shale gouge ratio (SGR) and σNeff for these faults were computed, and a calibration of the relationship between SGR and Pb across varying σNeff ranges was conducted to define the sealing failure envelope. This calibration reveals distinct fault sealing failure envelopes at different σNeff intervals, underscoring the significant impact of σNeff on fault sealing capacity. Consequently, an improved SGR parameter (ISGR) was proposed to incorporate both the fault rock's clay content and the influence of σNeff on fault sealing. By plotting ISGR against Pb, fault sealing failure envelopes were established, and a relationship between fault sealing capacity and ISGR was formulated. This relationship provides a novel means to evaluate the Pb sealable at specific ISGR values. Comparisons of the ISGR algorithm with other algorithms demonstrate a superior correlation with seal capacity in our samples. The fault sealing capacity of drilled fault-bounded traps was evaluated using this relationship, and the predicted hydrocarbon column heights are in close alignment with actual measurements, validating the reliability and accuracy of the ISGR algorithm in fault sealing evaluation. The consideration of both clay content and σNeff in the ISGR parameter and the associated calibration method makes it particularly suitable for assessing the fault's sealing capacity in diverse sand-clay sequences with varying strike and burial depths.

The research on fault and structural trap of the Weixinan Sag, Beibuwan Basin, South China Sea

The Weixinan Sag in Beibuwan Basin is a pilot area of the offshore exploration and development integrated technology. The main oil bearing layers, first member of Liushagang formation and third member of Weizhou formation, develop many fault systems and structural traps. The key factors of the offshore exploration and development integrated technology are”the fault research”and “the effectiveness of structural trap”. Fault research includes the study of the geometry, dynamics, kinematics characteristics of fault, and the division of fault system. The effectiveness of structural trap include analogical studies on the structural characteristics of traps, quantitative studies on fault lateral sealability, fault vertical sealability, and prediction technology of oil column height. Synthesizing the relationship of the law of oil and gas distribution,the differential fault system in the internal of the No. 2 fault zone, and the effectiveness research of traps, the fault-controlled reservoir laws and the dominant fault-controlled reservoir mode are obtained. The research on fault and trap of offshore integrated exploration and development has been successfully applied in the Weixinan Sag. The 37 of 45 development evaluation wells have been drilled successfully and the drilling success rate is 82%. It has promoted the ODP(original drilling project) implementation of 5 oilfields, the adjustment implementation of 8 oilfields and made important contribution to the increase of reserves and production in the Weixinan Sag.

Three-dimensional internal multiple elimination in complex structures using Marchenko autofocusing theory

Internal multiples are commonly present in seismic data due to variations in velocity or density of subsurface media. They can reduce the signal-to-noise ratio of seismic data and degrade the quality of the image. With the development of seismic exploration into deep and ultradeep events, especially those from complex targets in the western region of China, the internal multiple eliminations become increasingly challenging. Currently, three-dimensional (3D) seismic data are primarily used for oil and gas target recognition and drilling. Effectively eliminating internal multiples in 3D seismic data of complex structures and mitigating their adverse effects is crucial for enhancing the success rate of drilling. In this study, we propose an internal multiples prediction algorithm for 3D seismic data in complex structures using the Marchenko autofocusing theory. This method can predict the accurate internal multiples of time difference without an accurate velocity model and the implementation process mainly consists of several steps. Firstly, simulating direct waves with a 3D macroscopic velocity model. Secondly, using direct waves and 3D full seismic acquisition records to obtain the upgoing and downgoing Green’s functions between the virtual source point and surface. Thirdly, constructing internal multiples of the relevant layers by upgoing and downgoing Green’s functions. Finally, utilizing the adaptive matching subtraction method to remove predicted internal multiples from the original data to obtain seismic records without multiples. Compared with the two-dimensional (2D) Marchenko algorithm, the performance of the 3D Marchenko algorithm for internal multiple predictions has been significantly enhanced, resulting in higher computational accuracy. Numerical simulation test results indicate that our proposed method can effectively eliminate internal multiples in 3D seismic data, thereby exhibiting important theoretical and industrial application value.

A novel method for petroleum and natural gas resource potential evaluation and prediction by support vector machines (SVM)

Petroleum and natural gas resources (PNGR) are some of the major forms of fossil energy that are important for the development of industry and energy security. Along with the growing demand of petroleum consumption and the requirement for enhancing drilling success rate, reducing the exploration risk and saving exploration cost, prediction method for PNGR potential with high accuracy and wide practicability is needed. However, the existing PNGR evaluation and prediction methods based on traditional statistical principles are far from meeting the requirements of the present petroleum exploration and exploitation. Therefore, this study introduces a novel method for PNGR potential prediction by applying support vector machines (SVM) in the context of the rapid development of artificial intelligence and machine learning. This novel machine learning methodology first proposed a combination of support vector classification (SVC) for hydrocarbon accumulation probability prediction and then support vector regression (SVR) for reserve abundance prediction. The combining use of classification and regression model can fully utilize the professional knowledge of petroleum geology and the powerful data processing capabilities of machine learning algorithms and hence significantly improve the performance of the method. Furthermore, the dataset is set based on petroleum geology knowledge with the feature variables of source rock, sandstone reservoirs, sealing capacity and hydrocarbon migration, whose distribution are predictable and thus ensures the predictive effect in practical petroleum exploration. The results show that the testing accuracy of the hydrocarbon accumulation probability evaluation model by SVC ranges from 80% to 100% with an average of 88.92%. The performance of the SVR model for evaluating reserve abundance also performs well with the highest correlation coefficient of 0.767. In addition, several validation ways are applied for testing the reliability and stability of the model. For a hold-out test for a new zone, the model provides precise prediction of hydrocarbon accumulation probability and reserve abundance with an accuracy of 72.5% and a correlation coefficient of 0.744. The evaluation metric of the F1-score shows an average of 0.91 for the SVC models, the 4-fold cross-validation shows an average correlation coefficient of 0.663 for SVR model, which indicates the good performance of the SVC and SVR model. To conclude, this study not only provides an intelligent ML method system for PNGR potential precisely evaluation and prediction with the combination of SVC and SVR which is firstly used by application of ML in petroleum industry field, but is also significant for the application of ML in petroleum and natural gas exploration and exploitation.

Exploring for groundwater in sub-Saharan Africa: Insights from integrated geophysical characterization of a weathered basement aquifer system, central Malawi

Study RegionMkonga village, ∼35 km southwest of the capital city of Lilongwe on the central plains in Malawi, Africa, located at the crest of a local topographic-high characterized by crystalline basement. Study FocusGroundwater aquifer systems in the shallow buried crystalline basement are geologically complex reservoir targets with historically low drilling success rates. Understanding the basement weathering profiles and their implications for aquifer architecture is crucial for drilling productive wells. This is particularly critical in developing countries where water demands are rising. This study employs an integrated approach of 2-D seismic reflection and 2-D electrical resistivity imaging, constrained by borehole data to characterize the local basement aquifers in the crystalline-dominated terranes of central Malawi. New Hydrological Insights for the RegionThe integrated geophysical and borehole data reveal a layered weathering profile: shallow thin laterite and sub-lateritic layers, the saprolite, the saprock, and the fractured/fresh basement. We identify four potential water-bearing zones consisting of the base of the sub-laterite layer, the saprolite, the saprock and the fractured basement. The most productive boreholes are those that intersect low resistivity anomalies (< 20 ohm-m) that are collocated with strong but discontinuous reflectors. These targets are interpreted to represent water-bearing zones that connect the saprolite and saprock to recharge pathways at the base of the sub-laterite.

Effective Water Injection Development Test for Rolling Outward Expansion of Low-grade Reservoir

The development of ultra-low permeability reservoirs in the oilfield mainly involves a large proportion of ultra-low permeability and it is difficult to recover reserves because of scattered distribution, low reserve abundance, poor reservoir physical property, and great development difficulty as well as low production intensity, rapid production decline, and low stable production of oil wells. In order to speed up the development of undeveloped reserves and explore the effective technical approach to solve problems in low permeability and difficulty in recovering reservoirs, we carried out the effective water injection development test in the B1 test area. In this paper, in-depth research has been carried out in reservoir geological understanding, development well pattern design optimization, and advanced water injection technology research. Finally, a set of effective production technologies for low abundance reserves in complex geological conditions are formed, effective production in B1 Block that was hard to recover reserves is realized, the drilling success rate is improved greatly, and well pattern design optimization is achieved, advanced water injection efficient development technologies for low abundance reserves blocks are also developed. The demand for rolling production can be gradually extended to other oilfields, which has certain reference significance for the development practice of peripheral oilfields and similar small complex fault block oilfields.

Research and application of 5D seismic prediction technology

With the development of wide orientation, wide band, and high-density acquisition and processing technology, the original 3D (time, line number, and track number) seismic data have expanded to two dimensions — the addition of offset distance information and azimuth information, resulting in 5D seismic data. In this paper, we explore three aspects. Identifying microfaults through subazimuth superposition and poststack coherent body techniques; predicting fractures by means of prestack anisotropy, poststack dip, azimuth, coherence, and curvature; and inscribing river channels with pure longitudinal wave near-zero incidence angle reflection information — that is, the exploration of 5D seismic prediction techniques. Field applications in different types of geological bodies in the Lujiabao Depression and Ordos Basin proved that the 5D seismic prediction technology greatly improved the accuracy of reservoir prediction and the degree of implementation of microfaults, effectively guiding the deployment of wells and improving the drilling success rates.

Autonomous self-burying seed carriers for aerial seeding.

Aerial seeding can quickly cover large and physically inaccessible areas1 to improve soil quality and scavenge residual nitrogen in agriculture2, and for postfire reforestation3-5 and wildland restoration6,7. However, it suffers from low germination rates, due to the direct exposure of unburied seeds to harsh sunlight, wind and granivorous birds, as well as undesirable air humidity and temperature1,8,9. Here, inspired by Erodium seeds10-14, we design and fabricate self-drilling seed carriers, turning wood veneer into highly stiff (about 4.9 GPa when dry, and about 1.3 GPa when wet) and hygromorphic bending or coiling actuators with an extremely large bending curvature (1,854 m-1), 45 times larger than the values in the literature15-18. Our three-tailed carrier has an 80% drilling success rate on flat land after two triggering cycles, due to the beneficial resting angle (25°-30°) of its tail anchoring, whereas the natural Erodium seed's success rate is 0%. Our carriers can carry payloads of various sizes and contents including biofertilizers and plant seeds as large as those of whitebark pine, which are about 11 mm in length and about 72 mg. We compare data from experiments and numerical simulation to elucidate the curvature transformation and actuation mechanisms to guide the design and optimization of the seed carriers. Our system will improve the effectiveness of aerial seeding to relieve agricultural and environmental stresses, and has potential applications in energy harvesting, soft robotics and sustainable buildings.

Using electrical resistivity imaging technique for borehole calibration in selected communities in Asutifi North District, Ghana

This study has investigated the use of Electrical Resistivity (ER) technique for siting suitable groundwater points in selected communities within the Asutifi North District of Ghana where borehole drilling success rate has been low, leading to water shortages in the dry season. The study method employed involved 2D Electrical Resistivity Imaging (2D ERI) survey along existing boreholes in the area using the dipole-dipole array and correlating the outputs with existing 1D Vertical Electrical Sounding (1D VES) data and its corresponding borehole logs of the area to delineate the potential groundwater zones. The results from the 2D ERI survey showed the potential groundwater zones to be at depths of 14.7 to 58.9 m with resistivity values ranging from 2.08 to 156 Ωm while that for the 1D VES were at depths of 20 to 60 m with resistivities ranging from 67.10 to 545.28 Ωm. Also, the delineated potential groundwater zones from the 2D ERI showed a positive linear correlation with the observed aquifer zones from the borehole logs at a correlation coefficient (R2) of 0.72, whereas no correlation was observed when the observed aquifer zones from the borehole logs were compared to potential groundwater zones from the 1D VES data. Additionally, the 2D pseudo-sections from the 2D ERI survey aided in categorising the different potential groundwater zones in the area as good, moderate, fair and poor. Thus, the 2D ERI technique provided more detailed information on the subsurface in the area than the 1D VES approach and would be more reliable for subsequent groundwater exploration projects in the area and similar geological terrains.

Application of Forward Modeling in Putaohua Oilfield

Putaohua Oilfield is bounded by the large fault on the south side of Pu A1 Well. It is divided into Pubei and Punan development zones on the plane. It is an oilfield that has been developed by water injection for more than 30 years. With the increase of development time, the water content of oil wells increases rapidly, and the oil production of the oilfield decreases rapidly,In order to realize the study of petroleum geological potential in this area, find out the favorable target area for well layout, and effectively improve the drilling success rate,first of all, we need to do forward modeling for the study area to lay a solid foundation for subsequent research. This paper analyzes the change characteristics of seismic wave frequency attenuation attribute in reservoir oil and gas, and applies it to the study of reservoir oil and gas prediction in Putaohua Oilfield.

Coupling relationship between current in-situ stress and natural fractures of continental tight sandstone oil reservoirs

We have integrated rock mechanics and acoustic experiments, full-wave array acoustic testing, formation microscanner image logging, and hydraulic-fracturing data to evaluate the coupling relationship between current in-situ stress and natural fractures. We used the data of the Yanchang Formation in the DL block of the western Ordos Basin, China, as an example. Our results find that the Yanchang Formation mainly develops high-angle fractures and vertical fractures. Furthermore, the in-situ stress state of the target sandstone strata satisfies [Formula: see text]. Nearly vertical and high-angle fractures are formed in the environment when [Formula: see text] is the maximum principal stress. Therefore, the current in-situ stress state of the target layer matches the induced fractures (longitudinal tensile-induced fractures) and natural fractures. As the buried depth increases, the difference between the horizontal maximum and minimum stresses ([Formula: see text]) has a tendency to first decrease and then increase, and its conversion depth is approximately 2000 m. Natural fractures are not developed in the distributary bay (the lowest horizontal stress area) and the thick sand area in the middle of the main river channel (the largest horizontal stress area). Natural fractures are mainly developed on the two wings of the main channel, and their horizontal stress is approximately 2–4 MPa lower than the central part of the main channel. We determined a correlation between fractures and sedimentary facies, and we have an important reference value for improving the drilling success rate of tight oil reservoirs. Furthermore, our study provides insights into the prediction of fractures and sweet spots for further exploration and hydraulic fracturing activities in the studied area and elsewhere in continental tight sandstone reservoirs.

Seismic Wave Field Anomaly Identification of Ultra-Deep Heterogeneous Fractured-Vuggy Reservoirs: A Case Study in Tarim Basin, China

Ultra-deep (7500–9000 m) Ordovician tight limestone heterogeneous fractured-vuggy reservoir is an important target of FuMan Oilfield in Tarim Basin. The strike-slip fault controlled reservoir is related to formation fracture and dissolution caused by geological stress. The seismic wave-field anomaly characteristics with different energy and irregular waveform are displayed in the seismic profile. Accurate identification of fractured-vuggy reservoirs wrapped in tight limestone is the direct scheme to improve production efficiency. Therefore, a new combination method flow of seismic wave-field anomaly recognition is proposed. In this process, the seismic data must be preprocessed initially, and on this basis, robust formation dip scanning is carried out. Secondly, the dip data is applied to the transverse smoothing filter to obtain the formation background data. Eventually, the seismic wave-field anomaly data is the residual between background data and original seismic data. This method has been applied in blocks with different structural characteristics and can effectively improve the resolution of strike-slip fault controlled reservoirs. Based on the results, the drilling success rate is increased to more than 95%, and the high-yield rate of oil tests is increased to 75% in 2021. Multiple applications indicate that the method is robust and can be popularized.

Evaluation and application of conductivity of strike slip faults in China Shunbei reservoir, Tarim Basin

Shunbei reservoir in Tarim Basin is a typical ultra-deep carbonate reservoir with fault-fracture systems. The present in situ stress field has an essential influence on the permeability of fault-fracture systems. Therefore, it is of great significance to study the in situ stress field and permeability of the fault-fracture systems for drilling success rate and acid fracturing effect after drilling. Based on the data of regional seismic reflection and coherence, 3D geological models of reservoirs in Shunbei 1 and 5 fault zones are established. Through the logging data of typical wells, the size and direction of in situ stress are determined. Based on the finite element method and damage mechanics theory, the slip tendency coefficients of different parts of the fault-fracture systems are simulated and calculated. The numerical simulation results are consistent with the drilling history of typical wells. The critical slip tendency coefficient is 0.1 in Shunbei 1 fault zone and 0.3 in Shunbei 5 fault zone. Drilling the fault planes in the critical stress state can improve the drilling effectively and obtain the ideal well production. This study provides a new idea for the efficient development of the Shunbei ultra-deep fault-controlled reservoir.

Evaluation of Anti-Mullerian Hormone Predictive Value and Antral Follicle Count in the Success Rate of Ovarian Drilling in Polycystic Ovary Syndrome

Background: Laparoscopic ovarian drilling (LOD) is recommended for the treatment of women with polycystic ovary syndrome (PCOS) resistant to clomiphene citrate. Objectives: This study aimed to evaluate the effect of ovarian drilling on the serum levels of anti-mullerian hormone (AMH), androgens, and the number of antral follicles. Methods: This was a pre- and post-clinical trial performed on 30 infertile women with PCOS resistant to clomiphene citrate. Patients underwent standard laparoscopic ovarian drilling. Serum levels of AMH and androgens and antral follicle count (AFC) were surveyed before LOD and three and six months after LOD. The ovarian ovulation rate in each month was also monitored for six months. Then, the association between changes in these parameters, especially the level of AMH, and postoperative ovulation was investigated. A P &lt; 0.05 was considered statistically significant. Results: The number of antral follicles three (3.00 ± 8.00) and six months (7.73 ± 4.14) after ovarian drilling showed a significant decrease compared to preoperative values (12.40 ± 4.02) (repeated-measures ANOVA, P &lt; 0.001). The mean AMH (6.78 ± 1.08 versus 12.25 ± 1.35; P = 0.005) and the antral follicle count (7.71 ± 0.54 versus 12.29 ± 0.67 and P &lt; 0.001) were lower in ovulation than in non-ovulation patients. The significantly more AMH reductions were seen in pregnant women (3.63 ± 5.61) than in non-pregnant women (3.63 ± 1.24) (P = 0.01). Conclusions: It may be possible to use the changes in AMH and AFC to predict the success rate of LOD.

Structural deformation characteristics and shale gas preservation conditions in the Zhaotong National Shale Gas Demonstration Area along the southern margin of the Sichuan Basin

The Zhaotong National Shale Gas Demonstration Area along the southern margin of the Sichuan Basin is located in the complex marine tectonic area of South China, where shale deformation and reformation are intense and the factors controlling sweet spots are complex, so the preservation conditions have an important impact on the enrichment of shale gas. In order to support the selection and evaluation of shale gas sweet spots in this area and improve the success rate of drilling, this paper carried out a geological survey on field outcrops. Then, based on drilling, mud logging and physical property test data, the structural deformation pattern and the regional deformation characteristics of this demonstration area were analyzed, and the development characteristics of formation joints and fractures, the sealing capacity of shale surrounding rock and the distribution characteristics of gas reservoirs were studied. Finally, the preservation conditions of shale gas in the Wufeng Formation of Upper Ordovician and the Longmaxi Formation of Lower Silurian were discussed. And the following research results were obtained. First, in the Zhaotong National Shale Gas Demonstration Area, three structural deformation patterns are developed from south to north, including trough type, equal amplitude type and baffle type, which are distributed in three major deformation zones, respectively, i.e., the shear deformation zone of Central Guizhou Uplift, the compression–torsion deformation zone of northern Yunnan–Guizhou Depression and the compression deformation zone of Southern Sichuan Depression. Second, three types of joints and fractures whose relationships with the direction of strata are high angle, middle–low angle and bedding intersection are developed in the Wufeng–Longmaxi formations and its overlying strata, and their occurrence characteristics are basically consistent with those of the three major deformation zones. Third, the shale of Wufeng–Longmaxi formations is thick in the north and thin in the south and possesses the preservation conditions of source–reservoir integration and self-sealing hydrocarbon accumulation. And combined with the sealing ability of the overburden strata and the roof and floor, its preservation conditions are overall better. Fourth, from the perspective of shale gas component, this area can be divided into three belts, i.e., methane, methane + nitrogen mixture and nitrogen from north to south. And the preservation conditions of shale gas are generally better in the north and worse in the south. In conclusion, the shale in the central–northern part of Zhaotong National Shale Gas Demonstration Area (compression deformation area and its southern margin) is the most favorable area because of its large shale thickness, weak reformation and deformation, bedding development of joints and fractures, good sealing performance and excellent preservation conditions. The compression–torsion deformation zone of northern Yunnan–Guizhou Depression in the central part is moderate in preservation conditions, and it is the relatively favorable area. The shear deformation zone of Central Guizhou Uplift in the southern part has poor preservation conditions, and it is a prospective area.

Landscape impacts of 3D-seismic surveys in the Arctic National Wildlife Refuge, Alaska.

Although three‐dimensional (3D) seismic surveys have improved the success rate of exploratory drilling for oil and gas, the impacts have received little scientific scrutiny, despite affecting more area than any other oil and gas activity. To aid policy‐makers and scientists, we reviewed studies of the landscape impacts of 3D‐seismic surveys in the Arctic. We analyzed a proposed 3D‐seismic program in northeast Alaska, in the northern Arctic National Wildlife Refuge, which includes a grid 63,000 km of seismic trails and additional camp‐move trails. Current regulations are not adequate to eliminate impacts from these activities. We address issues related to the high‐density of 3D trails compared to 2D methods, with larger crews, more camps, and more vehicles. We focus on consequences to the hilly landscapes, including microtopography, snow, vegetation, hydrology, active layers, and permafrost. Based on studies of 2D‐seismic trails created in 1984–1985 in the same area by similar types of vehicles, under similar regulations, approximately 122 km2 would likely sustain direct medium‐ to high‐level disturbance from the proposed exploration, with possibly expanded impacts through permafrost degradation and hydrological connectivity. Strong winds are common, and snow cover necessary to minimize impacts from vehicles is windblown and inadequate to protect much of the area. Studies of 2D‐seismic impacts have shown that moist vegetation types, which dominate the area, sustain longer‐lasting damage than wet or dry types, and that the heavy vehicles used for mobile camps caused the most damage. The permafrost is ice rich, which combined with the hilly topography, makes it especially susceptible to thermokarst and erosion triggered by winter vehicle traffic. The effects of climate warming will exacerbate the impacts of winter travel due to warmer permafrost and a shift of precipitation from snow to rain. The cumulative impacts of 3D‐seismic traffic in tundra areas need to be better assessed, together with the effects of climate change and the industrial development that would likely follow. Current data needs include studies of the impacts of 3D‐seismic exploration, better climate records for the Arctic National Wildlife Refuge, especially for wind and snow; and high‐resolution maps of topography, ground ice, hydrology, and vegetation.

A frequency-divided gas prediction technology based on resistivity constraint

The gas–water relationship in the Permian and Triassic biohermal beach reservoirs in the Sichuan Basin is complex, which results in a low drilling success rate and leads to sidetracking or even secondary sidetracking in some wells. Therefore, high-precision gas–water identification is the key to the drilling success rate. In this paper, the biohermal gas reservoir in the T work area of the eastern Sichuan Basin was taken as an example. Firstly, the frequency information of seismic data sensitive to gas bearing properties was exploited sufficiently by taking the deep/shallow resistivity information which is sensitive to gas–water discrimination as a constraint and the nonlinear algorithm as a bridge. Then, combined with the information of full-band relative wave impedance, a nonlinear mapping relationship between the logarithmic difference curve of deep/shallow resistivity and the seismic waveform was established, and the gas bearing properties of the reservoir were predicted. In this way, a post-stack gas prediction method was developed. Finally, field application and effect analysis were carried out. And the following research results were obtained. First, gas layer information indicated by deep/shallow resistivity not only has the function of verification well, but can be extracted as a priori information for the constraint of seismic data. Second, frequency division information increases the mapping relationship between multi-frequency data volume and the logarithmic difference of deep/shallow resistivity, and the colored inversion, as the more reasonable full-band relative-wave impedance seismic data, is more conducive to gas and water identification. Third, based on the nonlinear mapping relationship, the data volume of a gas sensitive factor was obtained, and the range of gas layers was quantified, so as to realize the quantitative characterization of gas bearing properties. It is concluded that the gas prediction technology developed in this paper provides an effective and practical post-stack gas prediction method, and its field application effect is good, presenting wide popularization and application prospects.

Improved methods for determining effective sandstone reservoirs and evaluating hydrocarbon enrichment in petroliferous basins

Geological uncertainty is the greatest risk in oil exploration. Most of the evaluation and risk assessment of exploration projects are characterized by the hydrocarbon enrichment evaluation of the target reservoir to avoid non-effective reservoirs. Based on experiments and detailed analysis of the hydrocarbon accumulation process, we propose a new criterion, namely reservoir hydrocarbon enrichment potential index, expressed as PI, for improved evaluation and assessment. According to the index PI, sandstone reservoirs are classified into four categories: Level IV, PI ≤ 0; Level III, 0 < PI ≤ 0.01; Level II, 0.01 < PI ≤ 0.1; Level I, 0.1 < PI ≤ 1. Level IV reservoirs are non-effective, whereas Level III, Level II, and Level I reservoirs are effective and their hydrocarbon enrichment potentials increase progressively. The recommended strategy is to prioritize the exploration of sandstone reservoirs in the order of Level I > Level II > Level III and avoid Level IV reservoirs. This strategy was applied to the Mesozoic sandstone in western Sichuan Depression, China, to demonstrate the method and workflow. Drilling success rate is positively correlated with the PI of the sandstone reservoir. The results of 153 wells drilled in western Sichuan Depression show the accuracy of the method to be 84.5%. Therefore, this method is useful for quick and effective scientific decisions on oil exploration projects, thus mitigating the risks in oil exploration projects.