Ying-Qiong Basin Research Articles

Intelligent risk identification for drilling lost circulation incidents using data-driven machine learning

In drilling operations, lost circulation (LC) poses a significant challenge, potentially leading to severe accidents such as overflow or blowouts if not accurately identified and controlled. This study introduces a method for identifying LC risk severity using data-driven machine learning and statistical algorithms, specifically demonstrated in the Ying-Qiong Basin of the South China Sea. The method begins with variance filtering to eliminate invalid data, followed by the application of the Pearson correlation coefficient to remove redundant data. This process results in the selection of 12 logging parameters out of the initial 38. Combined with indirect judgments of LC severity based on relevant prior knowledge, the data is labeled to construct the original dataset. A feature extraction and optimization method is proposed, which employs sliding time windows to extract 21 features. These features are then selected and optimized using a random forest algorithm to construct the optimal feature set. To enhance the controllability of the Extreme Learning Machine (ELM) model, the sparrow search algorithm is integrated. Additionally, several fitness functions are introduced for both regression and classification models, resulting in the development of the improved ELM (IELM) model. The dataset is split into training and test sets, and the performance of the IELM model is compared to that of the standard ELM and BP neural network models. The results indicate that the IELM model outperforms the other two, achieving an impressive test F1 score of 97.22 % for accurately identifying LC severity. Moreover, the model trained using the optimal feature set demonstrates higher accuracy and faster convergence. The proposed feature extraction and optimization method effectively increases the amount of information contained in the data, thereby enhancing the model's performance.

Experimental study of a multimechanism formation pressure prediction model influenced by shale content

The precise prediction of abnormally high-pressure formations has always been a hot topic in oil and gas exploration and development. In the Yingqiong Basin of the South China Sea, abnormally high-pressure formations are widespread, with narrow drilling safety windows and frequent accidents caused by the limited accuracy of formation pressure prediction. To improve the prediction accuracy of formation pressure, based on the characterization and classification method of the pressure forming mechanism of sediment and mechanics and considering the influence of shale content on pore pressure, in this study, soil consolidation acoustic experiments were carried out using real rock debris soil in a block of strata in this area. We obtained the response laws of parameters such as acoustic velocity and density under different pressure-forming mechanisms and established an acoustic density intersection chart exhibiting the influence of shale content. The experimental results show that under the same loading mechanism and conditions, the higher the shale content in the core is, the smaller the density, the smaller the acoustic velocity, and the smoother the trend line of the acoustic density intersection chart. When the shale content ≥0.5, under the unloading mechanism, the higher the shale content of the rock is, the further away the unloading trend line is from the loading trend line, and the greater the difference in the changes in the acoustic properties of the rock compared to the density properties. Moreover, the experimental conclusion also verified why the pressure formation mechanism in non-shale formations is difficult to determine. Based on the experimental results, the traditional Bowers model was improved, and a multimechanism formation pressure prediction model for the influence of shale content was established. The established model was validated and compared. The evaluation results showed that compared to the traditional model, the maximum prediction error of the multimechanism prediction model was reduced by approximately 20%, and the average prediction error was approximately 3%. This model effectively improved the prediction accuracy of the formation pore pressure.

Research on the Suitability of High-Density Leakage Plugging in Offshore High Temperature and High Pressure Wells

A large number of fractured formations are developed in the high-temperature and high-pressure formations of the Yingqiong Basin in the South China Sea. During drilling, the risk of lost circulation is ex-tremely high, which will cause complex downhole accidents and seri-ously affect the drilling speed.In order to realize safe and efficient plugging of HPHT Wells, the following studies are carried out in this paper: Firstly, the characteristics of leakage, types of leakage and plug-ging and prevention mechanism of HPHT formation in Yingqiong Ba-sin are clarified based on core and indoor rock mechanics experiments. Secondly, a simulated plugging evaluation device with high tempera-ture resistance of 180 °C and high pressure resistance of 20Mpa was in-vented and applied to accurately evaluate the reservoir leakage behav-ior in Yingqiong Basin. Finally, a series of anti-high temperature plug-ging agents adapted to different loss types are systematically selected for the first time for different formation fracture types and the plugging effect is evaluated. In this study, through mechanism research, device research and development, accurate evaluation, the shaft wall pressure equivalent increased to 0.1g/cm3 without leakage. It provides technical support for the subsequent ultra-high temperature and high pressure stratum with weak leakage and narrow pressure window.

A new model for evaluating rock drillability considering the rock plasticity and chip hold down effect caused by hydrostatic column pressure under high confining pressure

The Yingqiong Basin in the northern part of the South China Sea is a region with large natural gas reserves. However, the high formation pressure and hydrostatic column pressure of the extra-thick mudstone section in this area present significant challenges to drilling operations. The mudstone has high plasticity and is very hard, and its thickness accounts for only 40% of the total footage, which results in pure drilling time accounting for over 75% of the total drilling time. To accelerate the rate of penetration (ROP) in this area, this study investigates the rock mechanics characteristics of mudstone under high confining pressure through experimental methods. The study reveals that the strength of the mudstone increases rapidly with increasing confining pressure, and the critical transformation stress of bottom-hole mudstone is around 45 MPa. Moreover, a cylindrical-cutter micro bit was developed, and the drillability of mudstone was tested under high confining pressure and hydrostatic column pressure, which further confirms that 45 MPa is the critical stress for a sudden increase in mudstone's drillability. Based on multiple regression analysis, the acoustic interval transit time, hydrostatic column pressure, and argillaceous content were identified as strong correlation parameters for the drillability of plastic mudstones. A new model for evaluating rock drillability considering rock plasticity and chip hold down effect caused by hydrostatic column pressure was developed, which provides effective guidance for the optimal design of bits and drilling fluid density in the extra-thick mudstone formations of the Yingqiong Basin. This study provides theoretical and technical support for the economic and efficient development of high-pressure gas fields in this area.

Biomarkers reveal the terrigenous organic matter enrichment in the late Oligocene—early Miocene marine shales in the Ying-Qiong Basin, South China Sea

Biomarkers reveal the terrigenous organic matter enrichment in the late Oligocene—early Miocene marine shales in the Ying-Qiong Basin, South China Sea

Soil consolidation acoustic experiment and pore pressure prediction model establishment—taking the Yingqiong Basin as an example

To establish a pore pressure prediction model suitable for the Yingqiong Basin in the South China Sea. A new laboratory test method was designed to simulate the core consolidation process, and an acoustic experiment for soil consolidation was carried out to analyze various parameters and establish an abnormal pore pressure prediction model suitable for the target block. First, the cause of abnormally high pressure in the Yingqiong Basin is analyzed and identified, and a simulation experiment of stratum loading and unloading is performed. The soil consolidation, experimental equipment and experimental plan are designed. Several sets of experiments were carried out, the changes in various parameters during the experiment were analyzed and summarized, the pore pressure prediction model suitable for this area was standardized and established, and application verification and evaluation were carried out in some wells in this area. The results show that the prediction model is accurate and applicable, and the pore pressure can be predicted by the soil consolidation experiment method that the prediction accuracy is slightly better than the traditional prediction model. In this study, a feasible soil consolidation acoustic experiment method can be used to establish a rock mechanics experiment and a pore pressure prediction model without strict core rock. The experiments have proved the feasibility of this method and obtained two prediction models, including loading mechanism and unloading mechanism prediction models.

Active Depths of Main Faults in the Ying-Qiong Basin Investigated by Multi-Scale Wavelet Decomposition of Bouguer Gravity Anomalies and Power Spectral Methods

Active Depths of Main Faults in the Ying-Qiong Basin Investigated by Multi-Scale Wavelet Decomposition of Bouguer Gravity Anomalies and Power Spectral Methods

CO2 Fluid Flow Patterns near Major Deep Faults: Geochemical and 3D Seismic Data from the Ying-Qiong Basin of the South China Sea

CO2 and hydrocarbon fluids typically migrate from deeper layers into the shallow crust via large deep faults. Consequently, CO2, hydrocarbon, and water reservoirs tend to occur in traps near deep and large faults. In this study, we use structural and stratigraphic data to identify and predict CO2 and hydrocarbon gas reservoirs near major deep faults. In order to investigate how CO2 accumulates in the major deep faults of the Ying-Qiong Basin (YQB), we quantify the carbon footprint of this area by analyzing the No. 1 fault, the No. 2 fault, and the adjacent gas reservoirs. Using 3D seismic data and geochemical data, we determine how the fault structure affects the ambient CO2 enrichment on a given fault. Our results indicate that the LD10 and BD19 gas reservoirs have high inorganic CO2 contents, while the HK29 gas reservoir has a low organic CO2 content. Based on our analyses, we conclude that the gas source, fault activity, and fault structure control the CO2 accumulation in subsurface layers. While mantle-derived volcanic inorganic CO2 disperses upward along the main fault when a given fault is independent (i.e., it lacks secondary faults), the absence of additional vertical migration channels largely prevents the CO2 from travelling upward through thick mudstone cap rocks and collecting in shallow traps. These shallow traps are typically filled by shallow organic CO2 sources. However, parallel forward fault-step structures, such as secondary faults, can transport gas that is produced at deeper sources (such as CO2 generated by basement limestone) to shallower depths. If the hanging wall of a deep fault has many branching secondary faults, then these intersecting faults act as conduits that enable mantle-derived CO2 to travel vertically into shallow layers.

Sedimentary geochemical records of late Miocene-early Pliocene palaeovegetation and palaeoclimate evolution in the Ying-Qiong Basin, South China Sea

The sedimentary geochemical records of palaeovegetation and palaeoclimate variations in late Miocene-early Pliocene sediments in the Ying-Qiong Basin, South China Sea have been studied using higher plant-derived biomarkers, palynological records, trace elements, and macerals. Aliphatic biomarkers including oleanane, des-A-oleanane, bicadinanes, and C19 tricyclic terpane, and the vitrinite content of the kerogen, show a remarkable decline in the input of the main angiosperms from about 8.2 to 2.7 Ma, corresponding to the deposition of the upper Huangliu Formation (late Miocene) to the lower Yinggehai Formation (early Pliocene). Aromatic parameters including retene/(retene + cadalene), 1,2,5-TMN/1,3,6-TMN, 1-MP/9-MP and 1,7-DMP/(1,3- + 3,9- + 2,10- + 3,10-DMP) suggest that the upper Huangliu Formation received a greater gymnosperm contribution than older Miocene formations. Trace element ratios (Rb/Sr and Zr/Rb) and the proportion of alginite-amorphous macerals in the shales indicate that a cooler, more arid climate with less seasonal precipitation occurred progressively from about 8.2–2.7 Ma, as also supported by higher abundances of Pinus and Alnus and decreasing proportions of ferns in the flora. Lesser input of terrigenous higher plants and the variation in vegetation types occurred during a cooling climate that was likely associated with a weaker East Asian summer monsoon and uplift of the northern Tibet-Plateau from about 8.5 Ma.

EXPERIMENTAL STUDY ON WATER-GAS PERMEABILITY OF HIGH-TEMPERATURE AND HIGH-PRESSURE SANDSTONE GAS RESERVOIRS IN YINGQIONG BASIN

EXPERIMENTAL STUDY ON WATER-GAS PERMEABILITY OF HIGH-TEMPERATURE AND HIGH-PRESSURE SANDSTONE GAS RESERVOIRS IN YINGQIONG BASIN

Design and Application of Automatic Dust-free Convey Equipment for Heavy Medium Solid Material on Offshore Drilling Platform

The Yingqiong Basin, a large high-temperature and high-pressure gas field in the South China Sea, is one of the three high-temperature and high-pressure areas in the world. According to incomplete statistics, from 1984 to 2013, a total of 30 high-temperature and high-pressure exploration Wells were drilled in the South China Sea. According to the drilling situation, there were 4 ultra-high temperature and high-pressure Wells with temperatures over 200°C and mud gravity over 2.20sg. With the increasing demand for oil and gas in China, the drilling operations of HP/HT Wells are also increasing, which is the inevitable trend of the development of oil and gas drilling technology. Due to the high pressure of Wells, drilling fluid need to be weighted by additives during cementing operations. In the past, these operations on offshore platforms were all done by manual. Therefore, we developed a set of positive-negative pressure conversion type continuous conveying device which integrated a weight medium negative pressure cutting device. The device consists of negative pressure dust-free feeding system, negative pressure conveying system, positive and negative pressure continuous conveying system, dust removal system and automatic control and detection system. It can realize flexible pipeline transmission through negative pressure and positive pressure. The device contains a variety of detectors to detect the operation situation in real time, and the control system can realize the functions of automatic control and automatic fault alarm. The results of experiment and field application show that the device can meet the high demand of heavy medium transportation.

Palaeovegetation variation in response to the late Oligocene-early Miocene East Asian summer monsoon in the Ying-Qiong Basin, South China Sea

Late Oligocene-early Miocene palaeovegetation and palaeoclimate in the Ying-Qiong Basin, South China Sea were comprehensively reconstructed using higher plant-derived biomarkers, palynological records, clay minerals, and kerogen maceral compositions of shales. During the period from about 24.9–18.3 Ma, there are trends of higher relative abundances of plant-derived biomarkers in the younger sediments. Similarly, over this time period there are increasing amounts of tropical/subtropical angiosperms and pteridophytes in the younger sediments, and lesser amounts of temperate Pinus and Alnus species. The bloom of the dominant tropical-subtropical higher plants and the large influx of terrigenous organic matter during this period were likely associated with extra summer monsoonal precipitation under a warming climate. The establishment of the East Asian summer monsoon in the South China Sea is proposed at about 24.9 Ma in the late Oligocene, which is likely to have been caused by uplift of the northern Himalaya-Tibetan Plateau at the same time.

Experimental study on stress sensitivity of high‐temperature and high‐pressure sandstone gas reservoirs in Yingqiong Basin

AbstractPerforming stress‐sensitivity evaluation on a high‐temperature and high‐pressure gas reservoir is essential for correctly understanding the characteristics of physical property changes and reasonably designing the development scheme of a reservoir under stratum conditions. By focusing on six core samples with different physical properties in a gas field in the Yingqiong Basin, stress‐sensitivity experiments have been conducted along with mercury intrusion porosimetry and X‐ray diffraction measurements to study the relationship among porosity, permeability, and effective stress at a temperature of 140°C and effective stress ranging from 2 MPa to 70 MPa. Our results showed that the stress‐sensitivity curve characterized by three‐stage segmentation is primarily affected by average pore radius and mineral composition but has no direct relation with porosity and permeability. Meanwhile, the stress sensitivity of permeability is mainly related to the average pore throat radius and mineral composition of core specimen. The smaller the pore throat radius and the higher the clay content, the stronger the stress sensitivity of permeability. Under high‐temperature and high‐pressure conditions, the stress sensitivities of permeability and porosity can be characterized by power functions although the stress sensitivity of permeability is about 2–11 times higher than that of porosity.

Research on Technology of Drilling in High Temperature and High Pressure Gas Field in South China Sea

The HTHP (high temperature and high pressure) areas of the Ying-qiong Basin in south China Sea has the characteristics of high temperature, high pressure, many pressure steps and narrow safety density window. The severe geological conditions pose a serious challenge to safe drilling in HTHP environment. Through more than 20 years of technical research and field practice. A set of key drilling technologies suitable for HTHP areas in south China Sea have been formed, including: multi-genesis formation pressure prediction, HTHP drilling fluid system, safe cementing technology, ECD accurate prediction technology, and drilling speed increasing technology. The engineering practice of safe drilling in the HTHP area of the South China Sea improves the efficiency of operation and ensures safe drilling. At the same time, the key technology also provides guidance for offshore drilling in HTHP areas.

Well test analysis method for CO2 content gas reservoirs of Ying-Qiong Basin

Mid-deep formations of Ying-Qiong Basin are characterized as deep, tight, high-temperature, and overpressure, the fluids in which generally contain CO2, so high-pressure physical property parameters of natural gas and stress sensitivity of low permeability reservoir should be considered in the well testing method. Thus, based on the Standing-Katz chart, the high-pressure natural gas physical property parameter calculation method is optimized that are suitable for reservoirs containing CO2, and taking the influence of pressure on seepage into account, a well testing analysis model considering stress sensitivity is established. Results show that when CO2 content is lower than 5%, the most properly high-pressure natural gas physical property parameter calculation method is LXF method, when CO2 content is higher than 5%, the most properly method is BB method. During radial flow period, the pressure derivative curves of drawdown test goes upwards gradually with the duration of production, and the greater is the stress sensitivity factor, the shorter is the distance between the pressure curves and the pressure derivative curves. While as for buildup test, the pressure derivative curves goes downwards gradually with duration of shut-in, and the greater is the stress sensitivity factor, the greater is the distance between the pressure curves and the pressure derivative curves.

Pre-drilling prediction techniques on the high-temperature high-pressure hydrocarbon reservoirs offshore Hainan Island, China

Decreasing the risks and geohazards associated with drilling engineering in high-temperature high-pressure (HTHP) geologic settings begins with the implementation of pre-drilling prediction techniques (PPTs). To improve the accuracy of geopressure prediction in HTHP hydrocarbon reservoirs offshore Hainan Island, we made a comprehensive summary of current PPTs to identify existing problems and challenges by analyzing the global distribution of HTHP hydrocarbon reservoirs, the research status of PPTs, and the geologic setting and its HTHP formation mechanism. Our research results indicate that the HTHP formation mechanism in the study area is caused by multiple factors, including rapid loading, diapir intrusions, hydrocarbon generation, and the thermal expansion of pore fluids. Due to this multi-factor interaction, a cloud of HTHP hydrocarbon reservoirs has developed in the Ying-Qiong Basin, but only traditional PPTs have been implemented, based on the assumption of conditions that do not conform to the actual geologic environment, e.g., Bellotti's law and Eaton's law. In this paper, we focus on these issues, identify some challenges and solutions, and call for further PPT research to address the drawbacks of previous works and meet the challenges associated with the deepwater technology gap. In this way, we hope to contribute to the improved accuracy of geopressure prediction prior to drilling and provide support for future HTHP drilling offshore Hainan Island.

莺琼盆地高温高压井气测录井特征研究

莺琼盆地高温高压井气测录井特征研究

Practice and Cognition of Midway VSP in High Temperature and High Pressure Field of South China Sea

Ying-Qiong Basin is a typical high-temperature and overpressure basin, which is the main battlefield of oil and gas exploration in South China Sea and has made great breakthroughs in recent years. During drilling process in high pressure, the relationship between the deep and the pressure is directly related to the drilling safety and costs. In order to improve prediction accuracy, the VSP operation is carried out through the midway, and three points have been obtained: 1) The VSP has a higher accuracy of the interface depth in certain depth range of the drill bit. 2) When the low-frequency trend prediction is accurate before the drill bit, interval velocity of the VSP inversion is consistent with the formation velocity. 3) The VSP pressure forecast is based on the inversion layer velocity and under-compaction pressure. If the velocity prediction is not accurate, the pressure forecast must be erroneous. If the pressure has other sources, the formation pressure is not accurate even if the inversion velocity is accurate. The application scope and exploration effect of midway VSP operation are summarized and applied to Ledong 10-1 block in Yinggehai basin, which realize the breakthrough in the field of high temperature overpressure and provide the basis for other similar exploration areas to do VSP operation.

Two innovative pore pressure calculation methods for shallow deep-water formations

There are many geological hazards in shallow formations associated with oil and gas exploration and development in deep-water settings. Abnormal pore pressure can lead to water flow and gas and gas hydrate accumulations, which may affect drilling safety. Therefore, it is of great importance to accurately predict pore pressure in shallow deep-water formations. Experience over previous decades has shown, however, that there are not appropriate pressure calculation methods for these shallow formations. Pore pressure change is reflected closely in log data, particularly for mudstone formations. In this paper, pore pressure calculations for shallow formations are highlighted, and two concrete methods using log data are presented. The first method is modified from an E. Philips test in which a linear-exponential overburden pressure model is used. The second method is a new pore pressure method based on P-wave velocity that accounts for the effect of shallow gas and shallow water flow. Afterwards, the two methods are validated using case studies from two wells in the Yingqiong basin. Calculated results are compared with those obtained by the Eaton method, which demonstrates that the multi-regression method is more suitable for quick prediction of geological hazards in shallow layers.

Productivity Analysis Method of Abnormal High-Pressure Gas Reservoir in Ying-Qiong Basin

Ying-Qiong Basin in the west of South China Sea contains plenty of abnormal high-pressure gas reservoirs, whose stress sensitivity is crucial for well productivity. To explore the influence of stress sensitivity on production, the variable outlet back pressure stress sensitivity experiments were applied to test core sample permeability under different burden pressure and obtain the relational expression of power function of core stress sensitivity. Afterwards, new productivity equation is deduced in consideration of reservoir stress sensitivity, and the affection of stress sensitivity on production is analyzed. The result demonstrates close link between stress sensitivity and productivity, since single well production decreases dramatically when reservoir stress sensitivity has been taken into account. This research is constructive for well-testing data interpretation in stress sensitive gas reservoirs.