Identification of fractures in tight-oil reservoirs: a case study of the Da'anzhai member in the central Sichuan Basin, SW China

The Da'anzhai Member of the Jurassic Ziliujing formation in central Sichuan is a typical tight-oil reservoir with porosity and permeability less than 2% and 0.1 × 10–3 μm2, respectively. Fractures in this formation are well developed in micro- and nano-scale. However, the factors that control the fracture distribution are unclear. Additionally, the uncomprehensive and ineffective identification and evaluation of fractures in the early stage of tight-oil development makes it difficult to meet the requirements of tight-oil development. In our work, we used cores, thin sections, and a scanning electron microscope (SEM) to study the influence of the microscopic rock composition, including the shelly grains, calcite grains, and clastic grains, on the fracture development. We found that the microscopic composition of shelly grains and calcite grains separately control the development of inter-shelly fractures and shelly fractures, and intergranular fractures, and tectonic fractures. Except for a small number of dissolution fractures found in mudstone, the fractures are not well developed in the formations with clastic grains. According to the characteristics of the development degree of fracture and the resolution of the well-logs, the fractures are divided into large scale, small scale, and micro-scale. By a newly established level-by-level constraints method, we systematically identified the scale, occurrence, filling characteristics, and development degree of fractures in the Da'anzhai member by well-logs. Moreover, a quantitative model is also proposed for identifying the angles and development degree of fractures. The results show that the scale of fractures can be effectively identified by the shapes and values of resistivity logs; the occurrence, development, and filling characteristics of fractures can be semi-quantitatively evaluated by the relative amplitude difference between the matrix resistivity (Rb) and formation resistivity (RT). The results are consistent with the interpretation results by formation micro-resistivity imaging (FMI) log, which further demonstrates that the level-by-level constraint method by conventional well-logs can be used to systematically and effectively predict the fracture characteristics in tight-oil reservoirs.

Experimental Investigation on Enhanced-Oil-Recovery Mechanisms of Using Supercritical Carbon Dioxide as Prefracturing Energized Fluid in Tight Oil Reservoir

Summary Fracturing is the necessary means of tight oil development, and the most common fracturing fluid is slickwater. However, the Loess Plateau of the Ordos Basin in China is seriously short of water resources. Therefore, the tight oil development in this area by hydraulic fracturing is extremely costly and environmentally unfriendly. In this paper, a new method using supercritical carbon dioxide (CO2) (ScCO2) as the prefracturing energized fluid is applied in hydraulic fracturing. This method can give full play to the dual advantages of ScCO2 characteristics and mixed-water fracturing technology while saving water resources at the same time. On the other hand, this method can reduce reservoir damage, change rock microstructure, and significantly increase oil production, which is a development method with broad application potential. In this work, the main mechanism, the system-energy enhancement, and flowback efficiency of ScCO2 as the prefracturing energized fluid were investigated. First, the microscopic mechanism of ScCO2 was studied, and the effects of ScCO2 on pores and rock minerals were analyzed by nuclear-magnetic-resonance (NMR) test, X-ray-diffraction (XRD) analysis, and scanning-electron-microscope (SEM) experiments. Second, the high-pressurechamber-reaction experiment was conducted to study the interaction mechanism between ScCO2 and live oil under formation conditions, and quantitively describe the change of high-pressure physical properties of live oil after ScCO2 injection. Then, the numerical-simulation method was applied to analyze the distribution and existence state of ScCO2, as well as the changes of live-oil density, viscosity, and composition in different stages during the full-cycle fracturing process. Finally, four injection modes of ScCO2-injection core-laboratory experiments were designed to compare the performance of ScCO2 and slickwater in terms of energy enhancement and flowback efficiency, then optimize the optimal CO2-injection mode and the optimal injection amount of CO2slug. The results show that ScCO2 can dissolve calcite and clay minerals (illite and chlorite) to generate pores with sizes in the range of 0.1 to 10 µm, which is the main reason for the porosity and permeability increases. Besides, the generated secondary clay minerals and dispersion of previously cemented rock particles will block the pores. ScCO2 injection increases the saturation pressure, expansion coefficient, volume coefficient, density, and compressibility of crude oil, which are the main mechanisms of energy increase and oil-production enhancement. After analyzing the four different injection-mode tests, the optimal one is to first inject CO2 and then inject slickwater. The CO2 slug has the optimal value, which is 0.5 pore volume (PV) in this paper. In this paper, the main mechanisms of using ScCO2 as the prefracturing energized fluid are illuminated. Experimental studies have proved the pressure increase, production enhancement, and flowback potential of CO2 prefracturing. The application of this method is of great significance to the protection of water resources and the improvement of the fracturing effect.

SUSTAINABLE DEVELOPMENT GOALS TO STRENGTHEN INDONESIAN PALM OIL DEVELOPMENT THROUGH INDONESIAN SUSTAINABLE PALM OIL (ISPO)

The palm oil development provides many advantages for Indonesia. One of which is that the development of Indonesian palm oil came fast and contributed a lot to the country's economic sectors. There are also other organic oil-based, such as jatropha, camelina, soybean and rapeseed. However, compared the palm oil to the other base of the organic oil materials, palm oil price outperforms the others oil-based because of the stability of the palm oil price. Palm oil benefits the Indonesian economy and the triple bottom line of John Elkington: people, planet, and profit. However, there is a critical issue with palm oil production. Its production is believed not to apply sustainability principles. Thus, it can damage and ruin the natural environment in Indonesia; for example, it damaged the area where the Sumatran tiger, Sumatran Orang Utan, and Borneo Orang Utan lived. Through the ministry of agriculture, the government established Indonesian Sustainable Palm Oil (ISPO) to answer this critical issue and recover the sustainability aspect of Indonesian palm oil. Abstrak: Indonesia beruntung karena dapat menikmati berbagai manfaat dari pembangunan kelapa sawit yang merupakan salah satu ciri dan keuntungan tersendiri yang Indonesia miliki, pembangunan kelapa sawit Indonesia sangat cepat dan pesat serta memberikan kontribusi yang tinggi terhadap negara melalui sektor ekonomi, jika dibandingkan dengan minyak nabati lainnya seperti : jathropa, camelina, soy bean dan rapeseed, kelapa sawit lebih unggul dari segi ekonomi yang mana dari segi harga lebih stabil jika dibandingkan minyak nabati dengan bahan baku lainnya. Minyak kelapa sawit memberikan berbagai manfaat bagi Indonesia selain daripada ekonomi juga terhadap triple bottom line sebagaimana dikemukakan oleh John Elkongton yakni people, planet dan profit sehingga dalam pemanfaatannya memberikan dampak yang baik meski begitu tetap saja dihadapkan dengan berbagai critical issue mengenai kelapa sawit. Dalam kegiatan produksi kelapa sawit diyakini bahwa belum mengedepankan aspek keberlanjutan yang kemudian berdampak terhadap kerusakan lingkungan di Indonesia. Kata Kunci: Indonesia, ISPO, Pembangunan Kelapa Sawit, Aspek Keberlanjutan, Triple Bottom Line