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Photocatalysts are mainly divided into two categories: one is that they have good response to sunlight and visible light, such as BiVO4 and Fe2O3; One is that it has its own defects and can not make full use of the energy converted by visible light. In recent years, a class of oxides have attracted much attention because of their good performance of visible light photocatalytic degradation of pollutants. People also have a strong interest in the research of compound oxides in pollutant degradation. In order to further clarify the photocatalytic mechanism of GCB composite samples, different capture agents were added to determine the main active species in the photocatalytic process. Only through the method of modification, the synergistic effect can enhance its photocatalytic activity. 1% g-C3N4/BiVO4(GCB) sample, drhb = 90.4%, the photocatalytic activity did not change significantly after adding IPA. After adding EDTA and VC, the photocatalytic activity decreased, drhb = 32.6% and drhb = 51%. Therefore, the experiments show that h+ and ·O2- are active species of GCB catalytic system, O2 is more important for RHB degradation.

In the past decades, horizontal directional drilling (HDD) has been successfully used to install various pipelines in different strata. However, construction accidents such as drill-burying and drill-sticking occur occasionally when pipelines installed by HDD method in an unstable stratum such as sand cobble stratum. Recently, HDD with dual drill pipes was used to install pipelines in unstable stratum, and the effect is significant. The law of cuttings migration for HDD with dual drill pipes is still unclear. Therefore, it is necessary to study the law of cuttings migration in reverse circulation with dual drill pipes. This study performs numerical simulations and experimental research on the cuttings-carrying process in reverse circulation directional drilling with dual drill pipes. Based on the assumption of dual concentric pipes, simulations of fluid-solid two-phase flows are conducted in different flow channels between the inner and outer drill pipes. An experimental cuttings-carrying model is then established. By combining the results of the numerical simulations and experimental investigation, the hydraulic parameters of the dual drill pipe system are optimized, and the rationalities of the drill tool design and the grading selection are validated. The results of this study provide a reference cuttings-carrying model during reverse circulation HDD with dual drill pipes.

Facies model is the basis of the geological model and determines the overall reservoir appearance. Due to limited data and extremely strong heterogeneity, the distribution of superior reservoir was hard to predict in a carbonate reservoir in the UAE, which often leads to empty wells and severe economic losses. With the help of neural network, a systematic study of sedimentation and diagenesis was carried out. The main controlling factors of reservoir properties were identified, and rock types were defined. Based on this, the facies model was established. The paper proposed a facies modeling method based on comprehensive sedimentary and diagenesis study assisted by neuro network. Firstly, sedimentary facies study was conducted to clarify the sedimentary background and reservoir geological architecture. Then, the diagenesis study was performed. In general, the main controlling factors for superior reservoir were deposition and cementation. Thirdly, rock type definition was established based on the knowledge of deposition, cementation and MICP data. Fourthly, the logs were processed, including quality control, normalization, etc. Then the sedimentary, diagenesis and rock type interpretation for the limited cored wells were propagated to the uncored wells using the neural network IPSOM method. The trend of deposition, cementation and rock type distribution were depicted. Finally, the rock type distribution was studied based on the trend of deposition and cementation, then the facies model was established. The study area was mainly proximal carbonate sedimentary environment, including the subtidal inner ramp and intertidal tidal flat. Diagenesis mainly included compaction, cementation, dissolution, and dolomitization. For the main reservoir, which was mainly the inner ramp deposits, SRT1 and SRT3 were defined as grain-dominated deposits with weak-medium cementation and medium-strong cementation, respectively. SRT5 was non-reservoir. For the secondary reservoir, it was intertidal environment, and mainly micrite dominated deposits. It only forms reservoir with dolomitization. SRT2 was defined as dolomitized micrite dominated deposits with medium-strong cementation, and the reservoir properties had been greatly improved. SRT4 was defined as weak-medium dolomitized micrite dominated deposits with strong cementation, with limited improvement in reservoir properties. SRT5 in this sedimentary environment was also defined as non-reservoir. With the neural network IPSOM method, the interpretation of deposition, cementation and rock type for the cored wells were propagated to non-cored wells and the trends were depicted. Then the rock type trend was finalized. Based on this, the facies model was established, and the cause of the dry wells was well explained. For this highly heterogeneous reservoir, the core analysis data was very limited. The cores were studied in detail, then the understandings were propagated to the uncored wells, which greatly enhanced the database. Based on this, a sedimentary facies model is established, which characterizes the distribution of high-quality reservoirs and provides a solid basis for oilfield development.

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In a Middle East oilfield, reservoirs are characterized by high temperature, high salinity, high CO2 / H2S content, and low pH, which leads to harsh corrosive environment. With development of the field, the increasing water cut and application of CO2-EOR technology have made tubulars face greater corrosion risk. Therefore, employing feasible anti-corrosion coating to corresponding part is one of the most effective technologies to mitigate downhole corrosion risk, reduce workover, and avoid potential HSE risk. Corrosion environment characteristics was thoroughly studied by reviewing production history, water chemistry, gas composition, downhole temperature and pressure, logging data, etc. Downhole corrosion condition was classified based on NACE standard RP0775-2005. Based on this, the field simulated corrosion tests were carried out on the self-healing coating in high-temperature and pressure autoclave. The self-healing coating was fabricated by loading slow-released MBT-LDH nanocomposites to the phenolic epoxy resin. For comparison, the similar experiment was also conducted on commercial phenolic epoxy coating and heavy-duty coating. The anti-corrosion performance and applicability of the coatings were characterized by SEM/EDS, FT-IR and EIS. Two main factors have been considered while evaluating the coating options, the first consideration is reliability and durability of the coating. If the coating is easily damaged during operation and transportation, its protective performance decreases after damage, which cannot be easily repaired again. The second consideration is the compatibility of the coating in a harsh downhole environment. Considering the above aspects, the self-healing coating, commercial phenolic epoxy coating and commercial heavy-duty were selected. After corrosion tests, a small amount of corrosion products can be observed on the commercial phenolic epoxy coating surface both in the simulated well head and bottom condition. There were no obvious morphology changes on the heavy-duty coating surface in both condition, however, chemical degradation of the coating was observed in well bottom condition. Notably, the self-healing coating appeared no peeling, bubbling and other defects in both conditions. There were corrosion products identified in the pre-destructed area of the coating, which attributed to the localized inhibition of the self-healing coating. This paper investigated the corrosion resistance coating technology, including coating selection evaluation, typical tubing thread area protection technique, coating chemical and physical property analysis and evaluation. The study also recommended coating applicability for the target reservoir. The results suggested that phenolic epoxy based self-healing coating show robust anti-corrosion performance and can be used in the downhole containing CO2 and H2S.

Marginal reserves are an important play in future energy development. Based on the statistics of China National Petroleum Corporation (CNPC), the low permeability and unconventional reservoirs occupied 92% of newly found proven reserves in China. To overcome challenges such as poor reservoir conditions, weak natural energy, low displacement efficiency, and insufficient single well production, CNPC has conducted years of research and operation to cost-effectively develop China's marginal reserves. To develop the marginal fields economically, it is required to maximize single well production, recovery and reservoir sweep with minimum CAPEX and OPEX reasonably. The production enhancement is realized by 3 key technologies, namely, sweet spot identification, multi-layered 3D short spacing horizontal well pattern, and volumetric fracturing techniques. The cost reduction is achieved by the full life cycle practice of utilizing "large cluster, factory" well design and field operation, drilling prognosis optimization, integrated intelligent surface system, and unmanned operation. CNPC cost-effective development mode is practical and successful, marginal fields characterized with heterogeneous, multi-layered oil-bearing intervals with poor continuity are being economically developed in China. By comprehensive geological study, fit-for-purpose technologies application, and geoscience-to-engineering integration, the fracture control degree of horizontal wells increased from 60% to more than 90% based on micro-seismic events, stimulated reservoir volume (SRV) increased by 46.8%, average cumulative oil production per well is more than 100 times than original production in the field. Fast and early cash flow is realized by minimum production facilities. The average drilling cycle is shortened by 61%, the surface facility construction time is reduced by 65%, and the average single well investment is reduced by 42%.

In the whole lifecycle of reservoir development, periodic intervention in wells is the daily work of reservoir management, which is essential to production maintenance and workover activity. The identification of actionable plan at well-by-well level is time consuming and inefficient, especially for reservoirs with a considerable amount of wells. Over-reliance on engineer experience also increase uncertainties over reliable plan. The workflow for candidate screening provides a systematic and efficient approach to dealing with this issue. Prior to commencing the process, reservoir static model and dynamic model were updated to meet recent reservoir performance. The first step was to identify potential wells in two ways, including the typical diagram indicating the relationship between production performance and reservoir properties, and the modified heterogeneity index method introduced by Del Castillo et al. After completing candidate recognition, diagnostic analysis was conducted to determine root causes through dynamic analysis of injection/production performance at well/pattern level. Finally, comprehensive evaluation and forecast for workover activities were carried out in terms of technical and economic aspects, which will facilitate appropriate decision making. This workflow has successfully been applied to a giant heterogeneous carbonate reservoir with gas cap. The identified candidates can be categorized into four types. The whole/partial gas cusping wells with a sharp/gradual increasing trend in gas-oil ratio (GOR) are influenced by gas cap. The gas channeling wells with uneven sweep efficiency are attributed to the injected gas overriding in heterogeneous reservoir. The water cusping wells with medium water cut are influenced by bottom aquifer. Accordingly, an integrated optimization plan is proposed to mitigate the outlined risks. The recompletion strategy with Autonomous Inflow Control Device (AICD) and sliding sleeves is recommended for gas/water cusping wells, and results are phenomenal in terms of segmented isolation of high GOR/water cut intervals and delaying gas/water breakthrough. The converting from gas injection to tapered water-alternating-gas (TWAG) through increasing the ratio of water-to-gas in a step wise process has been implemented for gas channeling wells, and an improved conformance is observed. The TWAG project appears to be promising because of high gas/water utilization efficiency and reduced gas cost. This methodological approach provides a generic workflow for conducting an integrated analysis of workover candidates screening and plan making. Reservoir performance will be monitored and maintained in order to ensure efficient reservoir management practice.