Green fields today mostly can be regarded as marginal fields and successfully developed. It covers the complete assessment of the oil and gas recovery potential from reservoir structure and formation evaluation, oil and gas reserve mapping, their uncertainties and risks management, feasible reservoir fluid depletion approaches, and to the construction of integrated production systems for cost effective development of the green fields. Depth conversion of time interpretations is a basic skill set for interpreters. There is no single methodology that is optimal for all cases. Next, appropriate depth methods will be presented. Depth imaging should be considered an integral component of interpretation. If the results derived from depth imaging are intended to mitigate risk, the interpreter must actively guide the process.
The current presentation date and time shown is a TENTATIVE schedule. The final/confirmed presentation schedule will be notified/available middle of October 2019. If we have learned anything from the North American experience, unconventional resources cannot be exploited by small incremental projects. If we are to be successful in developing these types of reservoirs, we have to make project scale operations work to bring these resources to market in a timely manner. A number of Eastern Hemisphere unconventional gas projects have raised interest, neared completion or are commencing deliveries.
Lu, Cong (Southwest Petroleum University) | Li, Junfeng (Southwest Petroleum University) | Luo, Yang (SINOPEC Southwest Oil & Gas field Company) | Chen, Chi (Southwest Petroleum University) | Xiao, Yongjun (Sichuan Changning Gas Development Co. Ltd) | Liu, Wang (Sichuan Changning Gas Development Co. Ltd) | Lu, Hongguang (Huayou Group Company Oilfied Chemistry Company of Southwest) | Guo, Jianchun (Southwest Petroleum University)
Temporary plugging during fracturing operation has become an efficient method to create complex fracture network in tight reservoirs with natural fractures. Accurate prediction of network propagation process plays a critical role in the plugging and fracturing parameters optimization. In this paper, the interaction between one single hydraulic fracture within temporary plugging segment and multiple natural fractures was simulated using a complex fracture development model. A new opening criterion for NF penetrated by non-orthogonal HF already was implemented to identify the dominate propagation direction of HF under plugging condition. Fracture displacements and induced stress field were determined by the three dimensional displacement discontinuity method, and the Gauss-Jordan and Levenberg-Marquardt methods were combined to handle the coupling between rock mechanics and fluid flow numerically. Numerical results demonstrate that the opening and development of NF are mainly dominated by its approaching angle and relative location. For a certain NF crossed by HF within plugging segment, HF tends to propagate along the relative upper part when the approaching angle is less than 90°, otherwise the lower part will be easier to open. The farther interaction position is away from HF tip, the easier NF with approaching angle less than 30° or larger than 150° can be open, and the outcome will be opposite if the approaching angle is larger than 45° or less than 135°. Higher approaching angle and plugging strength is necessary for expanding the position scope of NF that can be opened around HF. Under the impact of plugging, fluid pressure in HF plummets at the beginning of NF opening and keeps decreasing until NF extending for a certain distance or encountering secondary NFs. Fluid pressure drop occurs mainly in the unturned NF, together with the width of unturned NF is significantly lower than that of turned NF and HF. Sensitivity analysis shows that the main factors, such as geometry, aperture profile, and fluid pressure distribution, affecting the network progress under temporary plugging condition are the horizontal differential stress, NF position, approaching angle, plugging time, and plugging segment length. The simulation results provide critical insight into complex fracture propagation progress under temporary plugging condition, which should serve as guidelines for welling choosing and plugging optimization in temporary plugging fracturing.
Xue, Heng (China Zhenhua Oil Co., Ltd, State Key Laboratory of Oil & Gas Reservoir Geology and Exploitation Engineering, Southwest Petroleum University) | Huang, Zuxi (China Zhenhua Oil Co., Ltd) | Liu, Fei (Engineering Technology Research Institute, PetroChina Southwest Oil & Gas Field Company) | Liu, Pingli (State Key Laboratory of Oil & Gas Reservoir Geology and Exploitation Engineering, Southwest Petroleum University) | Wang, Hehua (China Zhenhua Oil Co., Ltd) | Zhang, Bo (China Zhenhua Oil Co., Ltd) | Cheng, Yi (China Zhenhua Oil Co., Ltd) | He, Bing (China Zhenhua Oil Co., Ltd) | Chen, Xiang (State Key Laboratory of Oil & Gas Reservoir Geology and Exploitation Engineering, Southwest Petroleum University)
Leakoff has been regarded as the key factor affecting live acid penetration distance and fracture etching patterns. The current leakoff coefficient model is insufficient to describe dynamic acid leakoff in the comprehensive matrix-vug-fracture medium. Furthermore, the carbonate reservoir medium is normally complex because of physical and mineral heterogeneity, which makes the acid leakoff process much more complicated. In order to increase the prediction accuracy of acid fracturing, the leakoff behavior of the matrix, wormhole & fracture and its’ related heterogenous etching patterns must be highlighted clearly.
In this paper, the leakoff experiments were performed under high temperature and high pressure (HTHP) to study the leakoff behavior for the matrix, wormhole & fracture respectively. Integrated with the experimental results, the wormhole leakoff model was developed considering the matrix and fracture medium. Based on the split rock, the conductivity of the acid etched fracture was studied to understand the effects of acid type, acid fracturing technique, closure stress, fracture roughness, mineral composition and structure on the conductivity. the integrated acid fracturing equation was developed through coupling the pseudo 3D fracture propagation model, wormhole leakoff model and the fracture heterogenous etching model. The solution was used to optimize technique parameters and predict acid fracturing effects in the carbonate reservoir.
According to the studies, the acid leakoff in the matrix agrees with Carter leakoff theory, while leakoff in the wormhole do not. The acid leakoff increases sharply with the wormhole propagation, and it has the quadratic relation with t^1/2 in the fracture. The mineral heterogeneity highly affects fracture etching patterns. Closed acidizing is an efficient method to enhance etching depth, therefore increasing fracture conductivity. The simulation results show that acid leakoff rates along the fracture length change locally and dynamically because of reservoir heterogeneity and the reaction between acid and rocks. The average leakoff rate on the fracture surface ranges in the magnitude of 10-4~10-3m/min, which tends to generate face-dissolution on the fracture surface. When the acid connects the natural fractures, the leakoff rate is sharply increased.
More than 10 wells’ acid fracturing proposals were designed based on the above works in the Upper Sinian Dengying Fm gas reservoirs in the Sichuan Basin of China. The simulated acid fracture length ranges from 23.4~42.6m, which is close to the well test results of 18.4~45.3m.
Zheng, Ma Jia (Southwest petroleum University) | Liu, Xin (Schlumberger Technology Services, Chengdu, Ltd) | Zhao, Jian Ping (PetroChina Southwest Oil and Gas Field Company) | Qiu, Xun Xi (Sichuan Shale Gas Exploration and Development Company Ltd) | Fang, Jian (CCDC Geological Exploration & Development Research Institute) | Wang, Xiong Fei (Schlumberger Technology Services, Chengdu, Ltd) | Zhao, Jing Kai (Schlumberger Technology Services, Chengdu, Ltd) | Geng, Gan (Schlumberger Technology Services, Chengdu, Ltd)
The Sichuan Basin is the major target for shale gas exploration in China because of its rich gas stored in unexploited black shale with multiple bed series. National Shale Gas Exploitation Areas have been established since 2012, the proved geological shale gas reserves is 9210×108 m3 and 90.25×108m3 annually output has been achieved by the end of 2017.
The operating Sichuan Basin shale gas area located in the major compression tectonic experienced multiple geological structure movements in Earth history, showing characteristics of high steep structure with faults greatly developed. It's proven that the key factors in exploiting these targets are well acknowledged by the efforts to land and expose the lateral within the sweet zone. To successfully place lateral in reservoirs from geological perspective must overcome challenges of high uncertainty structure identification to make soft landing and maximize horizontal exposure in the sweet zone.
While it comes to shale gas reservoir, to pave the way for fracture operation and achieve good well completion, the drilling requires a relative gentle well path, keeping well path inclination with limitation, which requires to make azimuth turning to achieve this.
To ensure the optimum placement of the well in sweet zone, the integration of rotary steerable drilling system (RSS) with borehole images measurements in real-time have been implemented with the employment of well placement technique.
The borehole image portrays structural profile while drilling whilst the rotary steerable drilling system provides accurate trajectory control. With the help of borehole image and proactive log correlation, the trajectory can be landed precisely into desired best quality reservoir, although the formation dip and actual target depth become much different with geological prognosis. During the lateral section, the trajectory was also controlled effectively in the high-quality reservoir despite of structural variation and reservoir property change. Through use of Fit-For-Purpose solution it effectively improves drilling efficiency and positively impacts well production. These achievements subsequently help to optimize wells deployment plan and wells with longer lateral horizontal section were planned for greater predictable production rate.
Li, Nianyin (Southwest Petroleum University) | Kang, Jia (Southwest Petroleum University) | Zhang, Qian (Southwest Petroleum University, Research Institute of Natural Gas Technology, PetroChina Southwest Oil & Gas field Company) | Wu, Yu (Southwest Petroleum University) | Zhang, Haotian (Southwest Petroleum University)
Considering characteristics of complex carbonate reservoirs (e.g., high depth, high temperature, and fracture cave development), this paper simulates expansion of the acid wormhole when combining diverting acid and a solid diverting agent for acid fracturing. Using the theory of reaction kinetics, tests of diverting acid reaction kinetics, and flow reaction experiments on the long core and parallel core, this paper presents tests of the acid–rock reaction for a mathematical model of acid diversion. On the basis of a rheological behavior test of diverting acid, we studied the influences of Ca2+ concentration, pH, fiber concentration, and temperature on acid system viscosity. Then, we established a mathematical model of changes in diverting acid viscosity under a multi-factor cooperative control mechanism. On the basis of the kriging method, we established a three-dimensional (3D) geological model involving a random normal distribution and spatial correlation of multi-fracture and pore-permeability properties. We used four models (acid rock reaction rate, viscosity change, 3D acid wormhole expansion, and fluid–solid coupling) of a complex system to study dynamic cooperation characterization of diverting acid and a solid diverting agent under multiple factors. Simulation results show that the temporary plugging of acid and expansion of acid wormholes are mutually restricted. The solid diverting agent blocked the fracture, and a dense filter cake formed at the start of the fracture; thus, the physical flow direction of diverting acid changed, the acid wormhole length increased, and filtration of diverting acid declined to improve the acid's effect. Diverting acid and solid diverting agent work more effectively together. This paper is novel because we consider the respective influences of Ca2+ concentration, pH, flow rate, diverting acid rheological properties, injection parameters, and solid diverting agent concentration on the synergistic steering of steering acid and a solid diverting agent. We then establish a mathematical model to reflect complex stratigraphic conditions and objectively describe the acid flow reaction. We also innovatively solve the problem of predicting acid wormhole expansion given complex fractures and uneven pore distribution. Findings provide a theoretical basis and technical support for the application of acid fracturing in complex carbonate reservoirs.
Li, Nianyin (State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University) | Yang, Ming (State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University) | Zhang, Qian (State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University) | Zhou, Hongyu (Natural Gas Research Institute of PetroChina Southwest Oil and Gas Field Company) | Zhai, Changjin (Zhanjiang branch of CNOOC Co. Ltd.) | Feng, Lei (CNOOC EnerTech-Drilling & Production Co.)
Matrix acidizing is an essential strategy to maintain or increase productivity or injectivity of hydro-carbon wells. However, for loose sandstone reservoirs, the rock skeleton structure is easily de-stroyed by acidizing with conventional acid systems, which results in sand production. Also, the precipitation of metal fluorides, fluorosilicates, and so forth that may occur during acidizing will cause secondary damage to reservoirs. Therefore, we propose a new multiple chelating acid system (NMCAS) with low damage and weak dissolution. The system consists of multiple weak acids, organic phosphonic chelators, anionic polycarboxylic chelating dispersants, fluorides, and other auxiliary additives. Its performance was measured through laboratory tests. First, the dissolution retardation effect and dissolution capacity of NMCAS were analyzed by long-term dissolution tests. Then, the changes of particle size and mineral composition of the rock powder before and after dissolution of NMCAS and a regular mud acid system were comparatively analyzed by a sieving analysis method and x-ray diffraction measurement. Third, the chelating abilities of the system on metal ions were analyzed by a titration method. Moreover, the improvement of seepage capacity was analyzed by a core acidification flowing experiment and scanning electron microscopy. Finally, the dissolution mechanism of the system was further analyzed by energy dispersive spectroscopy. Research results indicate that NMCAS has a good retardation effect and a moderate dissolution ability. After dissolution of rock powder with the proposed acid system, the changes in particle size were less than those of the conventional mud acid system. Also, it dissolved merely a small portion of the clay minerals, but increased the dissolution of quartz, feldspar, and other matrices. NMCAS can prevent secondary precipitation of metal ions during the acidizing process because of its strong chelating ability for calcium ions, magnesium ions, and iron ions. The permeability of sample cores was moderately increased, and they formed obvious dissolution channels; however, the rock skele-ton structure was not destroyed after acidizing with NMCAS. This is because the system reduced the dissolution of clay minerals with larger specific surfaces because of the adsorption effect (a relatively lower reduction in the content of the Al element) while enhancing that of such matrices as quartz and feldspar (relatively larger changes in the content of the Si element). NMCAS can dis-solve the cement appropriately while enhancing the dissolution of the matrices, which protects the rock skeleton structure of loose sandstone reservoirs. The proposed acid solution would be of value for removing formation plugging and increasing the production of loose sandstone reservoirs.
Wu, Jiwei. (East China University of Science and Technology) | Pan, Jiake. (East China University of Science and Technology) | Wang, Hualin. (East China University of Science and Technology) | Wang, Lixiang. (PetroChina Southwest Oil & Gas Field Company Chengdu Natural Gas Chemical General Plant) | Lan, X. (PetroChina Southwest Oil & Gas Field Company Chengdu Natural Gas Chemical General Plant) | Yang, L. (PetroChina Southwest Oil & Gas Field Company Chengdu Natural Gas Chemical General Plant) | Liu, Wenjin. (SJ Petroleum Machinery CO.SINOPEC)
With the flourishing shale gas exploitation produces more oil based mud (OBM) drill cuttings, the hardto-treat hazardous wastes burdens the local environment heavily. However, the problems of high energy consumption, high treating cost and high risk secondary contamination still remain unsolved for mainstream technologies such as thermal distillation, incineration and chemical extraction. Therefore, a new method and device based on cyclone desorption of high speed self rotation to dispose of OBM drill cuttings is put forward to overcome the challenge. The working process includes: viscosity reduction in heated gas; cyclone deoiling; condensation and recycling of exhaust; separation of oil and water in coalesce. It is found that the self-rotation speed of solid particles in a 3-dimensional rotating turbulent flow field of cyclone is as high as 2,000 to 6,000 rad/s which coexists with evolving speed of s The remarkable pulsing centrifuge force in the rotation and revolution coupling motion can enhance the desorption process of the oil so as to accomplish the separation and enrichment of oil and solid phase, and deep removal of organics from OBM drill cuttings.
Abughaban, Mahmoud (Saudi Aramco) | Alshaarawi, Amjad (Saudi Aramco) | Meng, Cui (CNPC Engineering Technology R&D Company) | Ji, Guodong (CNPC Engineering Technology R&D Company) | Guo, Weihong (CNPC Engineering Technology R&D Company)
Optimization of drilling parameters during drilling operations is a key component to obtain maximum rate of penetration (ROP) as well as minimizing the drilling cost. Advancement in computer technologies and communication are among the most important factors that can contribute to drilling optimization. In the current work, a novel rig advisory system is developed to continually improve ROP and the drilling performance. Conventionally, drillers apply drilling parameters (weight-on-bit, rotary speed and pump rate) according to past experience or to parameters specified in the drilling program. These parameters are usually kept constant over a long interval regardless of the formations being drilled. However, it is well-known that keeping constant drilling parameters to drive the bit will lead to redundant depth of cut (DOC), inducing stick-slip vibration that leads to low ROP, higher drilling specific energy (DSE), and potential damage to the bottom-hole assembly (BHA).
An intelligent drilling advisory system (IDAS), based on a soft-closed-loop solution with multiple regression analysis called optimum parameters global retrieval, has been established. Integrated with machine-learning methodology (Principal component analysis), the response of the drilling parameters with lithology changes was analyzed in real time. Additionally, the optimum control parameters direction were obtained from the gradient search and decision tree algorithms. This system monitored the relationship between the ROP and input energy delivered to the bit in real time, and calculated the optimized drilling parameters. The work presented how the IDAS procedures were applied in China, how the data was interpreted, and how optimum working parameters were obtained to guide drillers to improve drilling performance and reduce non-productive time (NPT).
IDAS has been introduced to hard formation drilling, which proved to be a success in real-time advisory aiding drillers applying proper working parameters for maximum ROP. Field applications of IDAS guidance showed significant ROP improvement compared to that of conventional drilling.
As an effective tool for further achieving the optimum DOC, a novel control system achieved satisfactory outcomes that overcome the drilling challenges in Saudi Arabia and China, which will serve as a step forward towards automated drilling operations.
Lai, Jie (Southwest Petroleum University) | Guo, Jianchun (Southwest Petroleum University) | Chen, Chi (Southwest Petroleum University) | Wu, Kaidi (Southwest Petroleum University) | Ma, Huiyun (Petro China Southwest Oil & Gasfield Company) | Zhou, Changlin (Petro China Southwest Oil & Gasfield Company) | Wang, Shibin (Southwest Petroleum University) | Ren, Jichuan (Southwest Petroleum University) | Wang, Zhi (Southwest Petroleum University)
As the most commonly used technology to exploit tight dolomite reservoirs, acid fracturing usually begins with injecting pad fluid to create rough-surface fractures, followed by pumping acid to form non-uniform etching on fracture surfaces. Thus, the etching pattern and acid fracture conductivity depend largely on initial character of rough-surface fractures. In this work, experiments were conducted to examine the effects of initial roughness and mechanical property of fracture surface on acid fracture conductivity.
Eight artificially split core samples were collected from tight dolomite outcrops and classified into three categories based on the surface topography and splitting force curve. Rough fracture surfaces were scanned utilizing the 3D laser scanner. Then, dynamic acid etching tests were conducted, varying the acid flow rate and acid-rock contact time. Besides, the roughness of fracture surfaces were measured utilizing the 3D laser scanner again. After that, acid fracture conductivity was determined. The effects of acid flow rate, acid-rock contact time, fracture surface topography and mechanical property on acid etching and acid fracture conductivity were discussed.
The experimental results demonstrated that the initial fracture surface topography and acid flow rate jointly controlled the acid etching pattern and the resulting acid fracture surface topography. The orientation of the fractures distributed on the fracture surface had significant effects on the acid fracture conductivity. Dissolved mass increased with longer acid-rock contact time. Longer acid-rock contact time brought higher acid fracture conductivity under low closure stress, while shorter contact time sustained higher acid fracture conductivity under high closure stress. Higher maximum splitting force referred to higher mechanical property, and more breaking stages referred to more microfractures developed. Rock samples with higher maximum splitting force and only one breaking stage exhibited higher acid fracture conductivity.
This paper provides a systematic method to study the effects of initial roughness and mechanical property of fracture surfaces on acid fracture conductivity. Compared with the results based on smooth-surface fracture, the experimental results based on rough-surface fracture can guide acid fracturing design and optimization in a more accurate way. Accordingly, a cost-effective stimulation outcome can be expected.