Wang, Wenjun (Petrochina Co. Ltd.) | Guo, Hongyan (Petrochina Co. Ltd.) | Huang, Youquan (Petrochina Daqing Oilfield Co. Ltd.) | Yu, Ying (Petrochina Daqing Oilfield Co. Ltd.) | Li, Donggang (Petrochina Daqing Oilfield Co. Ltd.) | Li, Qinggang (Petrochina Daqing Oilfield Co. Ltd.) | Sui, Hongyu (Petrochina Daqing Oilfield Co. Ltd.)
This paper introduces the first successful refracturing example of horizontal well in a tight volcanic gas reservoir of Xushen gas field. The well was fractured and put into production in 2008, with the accumulated gas production of 0.64×108 m3. Due to the limited technical conditions of the horizontal well-stage fracturing process at that time, only four fracturing stages have been carried out. the horizontal section of the volcanic gas reservoirs with more than 600 meters of the well was not fractured, leaving a large potential for increasing production. In 2017, based on the fine research of gas reservoirs, the refracturing optimization design, multi-stage perforation, fracturing and commissioning integrated tubular completion and the diagnosis control of complex fractures in fracturing construction, the refracturing job of the well is implemented successfully with a good result.
Xu, Jianguo (PetroChina Jilin Oilfield Company) | Zhao, Chenxu (PetroChina Jilin Oilfield Company) | Zheng, Jiangang (PetroChina Changqing Oilfield Company) | Xuan, Gaoliang (PetroChina Jilin Oilfield Company) | Zhang, Ruquan (PetroChina Changqing Oilfield Company) | Peng, Chong (PetroChina Changqing Oilfield Company) | Liu, Hongxia (PetroChina Jilin Oilfield Company)
In recent years, the investment of new area productivity construction in Jilin oil field is high, stabilized production becomes more and more difficulty, so the strategic center of oil field transfers to the refracturing of old well, however, the comprehensive water cut and recovery of old oil field is high, and the remaining oil dispersed, increasing production and increasing efficiency by refracturing becomes more and more difficulty. In order to deal with these challenges and realize the benefits of tapping in old area, the new idea of "group fracturing" was proposed basing on the concept of volumetric fracturing, starting from the reconsideration of reservoir geology, injection production unit for the smallest study unit, and integrating multiple fracturing method, we conduct a series of technical studies and field experiment in the old area of Jilin oilfield. The group fracturing technology series mainly includes the following: (1) The high strength positioning and plugging technique for reorientation fracturing; (2) Energy develop before fracturing and fast energy storage technique in fracturing; (3) Synchronous fracturing technique of multi wells; (4) Synchronous fracturing technique of oil and water well, reorientation fracturing technique of water well; (5) Fracturing combining with rapid profile control and water plugging technique; (6) "Factory-oriented construction".Since 2016, the group fracturing has carried out a total of 143 wells in 14 blocks in the old area, which has achieved good results. Compared with the conventional fracturing in the same area, the economic efficiency is increased by 10.2%, the oil increase of the single well is increased by 1 times, and the effective period of the measure is raised by 50%. The practice shows that the group fracturing technique is an effective measure to exploit the benefits of the old area in the low permeability oilfield.
Sun, Junchang (Research Institute of Petroleum Exploration & Development, PetroChina) | Zhang, Shijie (Xinjiang Oilfield Company, PetroChina) | Wang, Jieming (Research Institute of Petroleum Exploration & Development, PetroChina) | Guo, Hekun (Research Institute of Petroleum Exploration & Development, PetroChina) | Li, Chun (Research Institute of Petroleum Exploration & Development, PetroChina) | Xu, Hongcheng (Research Institute of Petroleum Exploration & Development, PetroChina) | Zhu, Sinan (Research Institute of Petroleum Exploration & Development, PetroChina) | Zhao, Kai (Research Institute of Petroleum Exploration & Development, PetroChina)
Compared with sandstones and carbonates, volcanic reservoirs are much more complex and heterogeneous due to the special eruption diagenesis mechanism, many types of rock lithology, various mineral compositions and a broad wide of pore sizes according to previous studies. Consequently, accurate characterization of volcanic reservoirs using the powerful nuclear magnetic resonance (NMR) logging requires a comprehensive laboratory NMR investigation of volcanic rock because currently used NMR interpreted methods were only developed for sedimentary reservoirs.
To gain an in-depth understanding of NMR characteristics of volcanic reservoirs with different lithology, a total of 108 low-permeability volcanic reservoir rock plugs from three large volcanic gas reservoirs named Xushen, Changling and Dixi, respectively, were prepared to perform NMR measurements and other related tests including CT scans, thin section petrography, mercury injection and mineral compositions analysis. The selected plugs comprise 9 types of lithology representing the main producing formation lithology of the three reservoirs. Specially, centrifuge tests were conducted with the maximum centrifugal forces up to 500 psi to explore the suitable capillary pressure for
Results indicate that, obviously different from sandstone and carbonate plugs, NMR porosity of volcanic plugs at fully brine-saturated state is strongly dependent on rock lithology. NMR porosities of trachyte, trachytic volcanic and granite porphyry are significantly less than the conventional ones measured by the Archimedes method, which means that, accurate identification of reservoir intervals lithology is a primary prerequisite before correct interpretations of NMR logging. Paramagnetic minerals mainly iron and manganese elements contained in volcanic reservoirs are the fundamental cause resulting in this abnormal phenomenon. The critical values of iron and manganese elements contents are approximately 2% and 0.06% by weight, respectively, above which the NMR porosity will be considerably less than the conventional one suggesting by inductively coupled plasma-atomic emission spectrometry (ICP-AES) tests on 14 representative plugs. Then, a new NMR porosity corrected formula was developed to improve interpreted quality of NMR logging. It was found that the suitable capillary pressure for determination of T2 cutoff of volcanic reservoirs is 400psi, 3 times larger than the commonly recommended standard (100psi) for sandstones. The calculated
The laboratory NMR results were used to interpret NMR logging of the Xushen reservoir of Daqing oilfield in eastern China and aided in detailed reservoirs evaluation. The outcome of beneficial intervals selection and high productivity well completion based on the NMR logging interpretation is very encouraging. This study indicated that a comprehensive laboratory NMR tests is very essential to successful application of NMR logging for complex reservoirs such as volcanic reservoirs.
Gong, Ke (China University of Petroleum) | Ye, Zhihui (China University of Petroleum) | Chen, Dong (China University of Petroleum) | Zhu, Dandan (China University of Petroleum) | Wang, Wanting (Xi'an Shiyou University)
The automation of lithology identification based on natural gamma, resistivity, neutron density and other well logging data is an important step to perform intelligent drilling/geo-steering. The current identification of lithology normally is based on the statistical results of the previous well logging data or on empirical methods, which may not be efficient or accurate. Therefore, a machine learning method is introduced here to improve the efficiency and accuracy of lithologic identification. With the development of a classification algorithm, the ensemble learning method becomes more influential since it can compensate the weak learning algorithm by using multiple learning algorithms to obtain better performance. The present research tries to identify different strata in complex sedimentary environment underground during the drilling process with a typical integrated learning method, the Adaboost algorithm, based on three wells in the Daan section, Longqian area of China. Typical single classification algorithms are used to identify the lithology, such as decision trees, SVMs (Support Vector Machines), and Bayes, etc. Comparing the results of single classifiers, the results of ensemble learning algorithm performed better than the selected single classifier. As such, the accuracy rate of lithology prediction can be increased from 66% to 90%.
Multicomponent joint inversion is an important technique for reservoir prediction using PP and PS seismic data. The addition of PS data is helpful to solve the problem of multiplicity and increase the precision of reservoir prediction. Based on 3D multicomponent seismic data of M area in Canada, the logging response characteristics of the reservoir are analyzed and the sensitive parameters are optimized. The PP and PS joint inversion, characteristic curve inversion and lithofacies probability simulation are integrated to increase the precision of reservoir prediction gradually. The application results show that, due to the reservoir prediction based on joint inversion, the top and bottom interface of oil sands reservoir and the distribution of interbed are described in detail. And important geophysical prospecting results are provided for oil sands development in this area.
Presentation Date: Monday, October 15, 2018
Start Time: 1:50:00 PM
Location: 213A (Anaheim Convention Center)
Presentation Type: Oral
Carbon dioxide (CO2) flooding is a mature technology in oil industry, which finds broad attention in oil production during tertiary oil recovery (EOR). After five decade’s developments, there are many successful reports for CO2 miscible flooding. However, operators recognized that achieving miscible phase is one of big challenge in fields with extremely high minimum miscible pressure (MMP) after considering the safety and economics. Compared with CO2 miscible flooding, immiscible CO2 flooding demonstrates the great potentials under varying reservoir/fluid conditions. A comprehensive and high-quality data set for CO2 immiscible flooding are built by collecting various data from books, DOE reports, AAPG database, oil and gas biennially EOR survey, field reports and SPE publications. Important reservoir/fluid information, operational parameters and project performance evaluations are included, which provides the basis for comprehensive data analysis. Combination plot of boxplot and histogram are generated, where boxplots are used to detect the special cases and to summarize the ranges of each parameter; histograms display the distribution of each parameter and to identify the best suitable ranges for propose guidelines.
Results show that CO2 immiscible flooding could recover additional 4.7 to 12.5% of oil with average injection efficiency of 10.07 Mscf/stb; CO2 immiscible technique can be implemented in light/medium/heavy oil reservoirs with a wide range of net thickness (5.2 - 300 ft); yet in heavy oil specifically reservoir (oil gravity <25 °API) with thin layer (net thickness< 50 ft) is better.
Liu, H. (Research Institute of Petroleum Exploration and Development, PetroChina) | Meng, S. (Research Institute of Petroleum Exploration and Development, PetroChina) | Zhao, Z. (Research Institute of Petroleum Exploration and Development, PetroChina) | Yan, J. (Research Institute of Petroleum Exploration and Development, PetroChina) | Yao, Z. (Research Institute of Petroleum Exploration and Development, PetroChina)
Over-developed oilfields in East China have gone through suffering situations induced by high cost in recent years. The trend of resource deterioration is irreversible and the deterioration leads to the increasing difficulties in oil and gas exploration and development. The rate of return-on-investment continually decreases resulting from over-rapidly increasing properties, and ever-rising facility depreciation and damage. The space for increasing income and seeking profit is further narrowed by low oil price. These oilfields now move into the period that has huge obstacles to increase profit, confronted with more difficulties in obtaining economic reserves and profitable production. Now the development in over-developed oilfields has stepped into double-high phase, meaning that to avoid ineffective or poorly effective measures and control the fundamental indices like the rise of watercut, natural decline, and so on play the key role in improving development profit. It is necessary to accelerate the build-up of production capacity and enhance reserve, production, and the rate of return-on-investment by actively reforming techniques for the formation of a series of new ones on enhancing oil recovery, as well as advancing the four-unified-into-one management mode of merging production and management, investment and cost, reserve increase and production build-up, and research and production. The concept of focusing on reserve and production must be further switched, meanwhile profit must be realized in all the ingredients of exploration and development during their whole processes, and efficiencies must be maximized. The burden of production and management is relieved, and the focus is switched to profit in an overall and complete way by further recognizing that investment today is tomorrow's cost and strictly controlling property scale to prevent its excessive increase.
Teng, L. (Northeast Petroleum University) | Song, H. (Northeast Petroleum University) | Zhang, S. (Liaohe Oilfield Company, CNPC) | Wu, F. (Liaohe Oilfield Company, CNPC) | Xu, D. (Liaohe Oilfield Company, CNPC) | Gong, Y. (Liaohe Oilfield Company, CNPC) | Jiang, Z. (China University of Petroleum) | Gao, H. (China University of Petroleum) | Wang, C. (China University of Petroleum) | Zhong, L. (China University of Petroleum)
In-situ combustion (ISC) has been investigated worldwide as a potential EOR process both for heavy oil and conventional oil, and there are some successful field applications such as industrial test in Suplacu and many tests in deep reservoir with low permeability. Most of heavy oil reservoirs recovered by In-situ combustion are known for favor reservoir properties such as limited layers (single layer is best) and appropriate heavy oil viscosity (usually hundreds to thousands of mPa•s). Obviously, it is challenging to recover multilayered heavy oil reservoirs by in-situ combustion method in consideration of heterogeneity between layers. For instance, Du 66 reservoir is a typical multilayered heavy oil reservoir in Liaohe Oilfield, it was not effectively recovered by cyclic steam stimulation (CSS in short) before 2005, and both oil production and OSR were unsatisfactory. There are no alternative but to test in-situ combustion for the purpose of improve oil recovery for such multilayered heavy oil reservoir. As a result, there are up to 91 well groups operated in inverted nine-spot pattern fireflood combined with CCS for production wells in past 10 years.
In this work, feasibility analysis and engineering design of in-situ combustion for multilayered D66 reservoir are primarily investigated based on reservoir engineering study and numerical simulation. Furthermore, recovery performance such as air injection profile and gas production and channeling are discussed based on field measurement and performance. Particularly, principles and treatment of gas channeling and casing collapse are discussed. Additionally, both experience and lessons are presented based on statistical results and typical cases.
The results show that considerable increase in oil production and improvement in ratio of oil production to steam injection (OSR in short) are observed at lower ratio of air injection to oil production (AOR in short). However, gas channeling occurs in some production wells in form of rapid increase in AOR, and it has significant effect on production performance. At the same time, casing collapse are found in many air injection wells, according remedial well treatment had to be carried out considering risk of high temperature, backfire and even explosion, and casing collapse has a much greater impact on injection performance and oil recovery. Therefore, investigation on gas channeling and profile control treatment of air injection wells were extensively carried out to eliminate gas channeling and casing collapse.
In summary, the principles and engineering design of in-combustion in multilayered heavy oil reservoir are much more complex than single layer reservoir. Gas channeling and casing collapse are two extremely difficult problems in such combustion process, which could be eliminated or weakened based on rational engineering design and effective technologies.
Noticeable progress in understanding the high efficiency of “foamy oil” in solution gas drive in heavy oil reservoirs has been made in recent years. However, “foamy oil” during CO2 flooding was still a special and novel phenomenon when CO2 flood asphaltic oil. The basic mechanism and corresponding numerical equation of seepage flow of ‘foamy oil’, in connection with CO2 flooding, have not been reported. This paper presented the mechanism analysis and simulation study that addressed this issue.
A new viewpoint of foamy oil during CO2 flooding was proposed with contrasting the similarity of ‘’foamy oil” during CO2 flooding front with that in dissolved gas flooding. During CO2 flooding the ‘’foamy oil” could form when CO2 contacted with oil because precipitated asphaltene could facilitate bubble nucleation, decrease the critical super-saturation and help in maintaining the dispersed gas flow by suppressing bubble coalescence, which similar to ‘foamy oil’ in depletion drive. Two main mechanisms were proposed. The first was enhancing oil recovery obviously by decreasing viscosity of crude oil, reducing interfacial tension, and swelling oil. The second mechanism was steady gas/oil mobility helping in maintaining high pressure in the reservoirs.
Then, the compositional model considering bubble nucleation, growth and coalescence and CO2 flowing characteristic was established, combining the advantages of “equilibrium model” with that of “dynamic model”. With the establishment of the model, the flowing characteristic of ‘’foamy oil” during CO2 flooding was regarded as the function of time and flow condition. The relative permeability curve and critical saturation of bubble were modified to determine the influence of “foamy oil” on oil recovery.
Taken one oil field in north China as example, the compositional model calculation results indicated that bubble was mainly located at the front of carbon dioxide flooding. High efficient flooding potential was achieved with “foamy oil” existed in carbon dioxide displacing front which were in accordance with the anomalously good performance in oil production. This method of calculating foamy oil properties would provide the basics for developing numerical simulation models of foamy oil flow during CO2 flooding.
Carbon dioxide (CO2) flooding is a mature technology in oil industry that finds broad attention in oil production during tertiary oil recovery (EOR). After about five decades of developments, there have been many successful reports for CO2 miscible flooding. However, operators recognized after considering the safety and economics that achieving miscible phases is one of big challenge in fields with extremely high minimum miscible pressure (MMP). Compared with CO2 miscible flooding, immiscible flooding of CO2 demonstrates the great potential under varying reservoir/fluid conditions. A comprehensive and high-quality data set for CO2 immiscible flooding is built in this study. Valuable guidelines have been concluded, and production prediction models are established to further assist the applicability of new projects for the first time. Results show that along with the current method in literature to find applicability guidelines, prediction models involved with important operation and production parameters help to increase the accuracy of CO2 immiscible applicabilities. Data involved in this study are checked for independence for feature selection before utilization. We also find that support vector machine could predict the enhanced oil production rate and CO2 injection efficiency better than multiple linear regression method based on the data set. Furthermore, the multiple linear regression method build an excellent model for the prediction of enhanced oil recovery with an accuracy of almost 100%.
A prediction model is a tool for decision making and problem solving that has been applied in variety of fields (e.g., medical science [1-3], meteorology , transportation [5, 6], business [7, 8], biology [9, 10], and chemistry [11, 12]) for further applicability evaluation. Eagle et al. built a prediction model to accurately estimate the risk of six month mortality after patients have been hospitalized for acute coronary syndrome (ACS), which provides guidance of the intensity of therapy to clinicians in clinical medicine . Gendt et al. established a numerical weather prediction model to help people to make plans for many activities (e.g., farmers to find the best time for harvest; pilots to schedule the safest path, etc. ). In a prediction model, prediction accuracy mainly depends on the methodology of prediction and the quality of data that fed into the model, which is one of the crucial indicator to evaluate the effectiveness of models that researchers spare no efforts to pursue as high of an accuracy as possible.