China has hundreds of thousands of oil and water wells, about 30% of which have been abandoned currently. If we can convert abandoned wells into geothermal wells, it will save lots of money and reduce drilling and completion time greatly. In this paper, six enhanced geothermal system (EGS) well layout schemes are proposed based on the utilization of abandoned oil–water wells and common oilfield well pattern. Here six common injection-production well patterns in oilfield are combined to hot dry rock (HDR) production and the heat extraction performance is simulated. The results show that the injection well number and the location of injection wells have critical influence on the heat extraction performance. Under the same total injection mass flow rate, the injection well number is the key factor and the fracture area is the secondary factor on heat extraction when the HDR energy is enough. For electricity generation, the life span is 20.2, 19.2, 19.0, 19.2, 18.2 and 13.9 years, and the heat extraction ratio is 65.83, 57.35, 65.96, 62.79, 59.30 and 43.09% from case 1 to case 6, respectively. For heating demand, the life span is 30.0, 30.0, 29.9, 30.0, 29.8, and 27.7 years, the heat extraction ratio is 78.91, 69.63, 77.02, 75.92, 72.27 and 58.94% from case 1 to case 6, respectively. The total injection mass flow rate and injection temperature also have a negative effect on the heat extraction performance. Case 1 (row parallel well layout), Case 3 (four-spot well layout) and Case 4 (five-spot well layout) are a good choice both for electricity generation and heating demand. This study provides good guidance for the selection and optimization of different EGS well layout.

Steering control algorithm plays an important role in a rotary steerable system for horizontal well drilling, including the determination of the well trajectory, vibrations, stability, durability among other variables. This work develops a control algorithm for three static push-the-bit rotary steerable systems (RSS^TSP) (TSP is the abbreviation of “three static push-the-bit”). Based on the structure, mechanism, and working process of the RSS^TSP, mechanical and mathematical models are proposed to determine the required steering force (amplitude and direction) to move the drill bit from a point to another. Additional equations are constructed to overcome the non-uniqueness and then compute the optimal forces for the three pads to achieve the required steering force. Moreover, a new control algorithm of RSS^TSP is developed, considering the steerability, stability, durability, favorable area, unfavorable area, maximum usable magnitude of steering force. The proposed control algorithm is also applied to a new RSS^TSP and tested on a GU-693-P102 well for validation. It is found that each pad force changes smoothly, the drilling tool is stable, and the well trajectory is consistent with the design, demonstrating that our proposed control algorithm is robust and effective for RSS^TSP for horizontal well drilling.

Wax deposition can reduce flow channel, increase the resistance and decrease fluid producing intensity in oil pipelines, which bring a critical operational challenge for the oil development. The prediction of temperature field and wax deposition location is the basis in thermal washing and wax removal. In this paper, the wells of sucker rod pump in Da Qing oil field is selected as the research object, a new method is proposed to predict temperature field and wax deposition location based on heat–fluid coupling method. The regularities of temperature distribution and wax deposition location are simulated with different fluid producing intensities and moisture contents. With the migration of produced liquid, the temperature decreases from bottom to upward, while the decline rate becomes less and less. With the increase of fluid producing intensity and moisture content, the temperature is increasing and the wax deposit location becomes shallower. In contrast to the calculated and measured results, the coincidences rate distribution is in the range of 95.61–97.86%. The results have a significance to the thermal washing plan formulation.

In this work, the intensive theoretical study and laboratory tests are conducted to evaluate the craters morphology via the flat-ended indenter test, relationship of indentation hardness (HRI) and uniaxial compressive strength (UCS). Based on the stress distribution, failure process and Mohr–Coulomb failure criterion, the mathematical mechanical models are presented to express the formation conditions of “pulverized zone” and “volume break”. Moreover, a set of equations relating the depth and apex angle of craters, the ratio of indentation hardness and uniaxial compressive strength, the angle of internal friction and Poisson’s ratio are obtained. The depth, apex angle of craters and ratio of indentation hardness and uniaxial compressive strength are all affected by the angle of internal friction and Poisson’s ratio. The proposed models are also verified by experiments of rock samples which are cored from Da Qing oilfield, the percentage error between the test and calculated results for depth, apex angle of craters and the ratio of HRI and UCS are mainly in the range of –1.41%–8.92%, –5.91%–3.94% and –8.22%–13.22% respectively for siltstone, volcanic tuff, volcanic breccia, shale, sand stone and glutenite except mudstone, which demonstrates that our proposed models are robust and effective for brittle rock.

Wax deposition in oil pipelines brings a critical operational challenge in the oil development, and the indirect thermal washing is a most common and effective method of wax cleaning. The temperature field in thermal washing is the basis for making a reasonable plan to wash and remove wax well. In this paper, the wells of sucker rod pump in Da Qing oil field are selected as research objects, a new method which is based on heat-fluid coupling method is proposed for predicting temperature field during the thermal washing process. The temperature field of the annulus of tubing and casing and the temperature field of the annulus of rod and tubing are simulated with different thermal washing parameters. In the indirect thermal washing, the temperature in annulus of tubing and casing gradually decreases from wellhead to the bottom, while the temperature in the annulus of rod and tubing increases from bottom to the wellhead. With the increase of temperature and flow rate of thermal washing fluid, the temperature in annulus of tubing and casing and the temperature in annulus of rod and tubing are both increasing, but the rise rate is different at different depths. Compared to the measured results, the coincidences rate is in the range of 93.67%–99.31%. The research results can guide effectively the thermal washing operation.

The strong heterogeneity of glutenite formations poses significant challenges for drilling optimization, including frequent bit failure, low rate of penetration (ROP), and high bit consumption. To address these issues, this study establishes a quantitative evaluation model for glutenite Reservoir Rock drillability by integrating fractal theory with experimental analysis. Based on fractal theory, artificial glutenite samples with different particles fractal dimensions were prepared by adjusting three key parameters: gravel content (20–90%), main particle size (0.25–12.5 mm), and grain size sorting (0.5–0.75). Microdrilling experiments were then conducted using a 32-mm-diameter PDC bit under a weight on bit (WOB) of 500–2000 N and a rotational speed of 55 r/min. Experimental results indicate that gravel content and grain size are the primary factors influencing the drillability of glutenite rock. As the gravel content increases and the main grain size enlarges, the difficulty of drilling significantly increases, resulting in extended drilling time. Notably, there is a strong correlation between particle’s fractal dimension and its drillability. The evaluation model correlating particle’s fractal dimension and drilling time, established through experiments, achieved a coefficient of determination (R²) of 0.9462 when applied in the Bohai Bay Basin. The study results can effectively guide bit selection and drilling parameter optimization for glutenite reservoirs.