A Solution to Sand Production from Natural Gas Hydrate Deposits with Radial Wells: Combined Gravel Packing and Sand Screen

Sand production is one of the main problems restricting the safe, efficient and sustainable exploitation of marine natural gas hydrate. To explore the sand-control effects of gravel packing, experiments that simulate hydrate extraction in the water-rich environment were conducted with designed hydrate synthesis and exploitation devices. Three sand control completion methods, including 120 mesh sand screen, 400 mesh sand screen, 120 mesh sand screen combined with gravel packing, are adopted. Sand and gas production rates were compared under different well types and sand control completion methods. Results show that the gas production modes of radial wells and vertical wells are almost the same at the same time due to the small experimental scale and high permeability. The sand production of the vertical well with gravel packing combined with a sand-control screen is 50% lower than that of the vertical well with sand-control screens only. Radial well with gravel packing combined with sand-control screens produced 87% less sand than screen mesh alone. The cumulative gas production and recovery rates of a radial well with the composite sand control method are better than those without gravel packing in the same development time.

Thermal Wellbore Failure Detection Case Studies: A High Temperature Multi-Finger Caliper Surveillance Approach

Cooling of thermal wellbores such as steam assisted gravity drainage (SAGD) and cyclic steam stimulation (CSS) wells, is a common prerequistite to allow deployment of logging instruments due to the temperature limitation of imaging instruments’ electronics (<150°C). This paper presents a memory caliper technology housed in a thermoshield that can perform at up to 220°C, with the acquired data used to evaluate the integrity of tubulars and completion items (metal loss, deposition, deformation, and gap/hole damage), negating the need for cooling before deployment. Two cases are presented. One is a SAGD well with liner screens across the lateral section. The memory multi-finger caliper was deployed using coiled tubing and the data were successfully obtained across the lateral section with a maximum recorded temperature of 169°C. The second example is a vertical well in a steam flood field. Because of the uncertainty over the downhole temperature at the time of the well intervention, a temperature sensor was deployed in surface read-out mode above the caliper. This ensured the 220° temperature limit of the caliper would not be breached, and a maximum temperature of 208°C was recorded. The data confirm the feasibility of acquiring high accuracy/high resolution data from thermal wellbores without having to resort to manipulative cooling techniques to attain a temperature below 150°C. Enlargement of a limited entry perforation (LEP) was observed in the horizontal well and buckling was clearly detected in the vertical well. The broad measurement range of the caliper – 1.85" – 7.2" – enabled both the tubing and liner to be logged in a single well intervention, which facilitated a swift resumption of of steam injection activities. Ultimately, the high temperature MFC's ability to minimize deliberate cooling the thermal wellsbore before deployment, has time and cost saving implications throughout the life cycle of the well. Much of the existing literature examining downhole data acquistion in thermal wells, for the diagnosis of wellbore integrity issues, has relied on technologies that are unable to withstand temperatures much greater than 150°C. The ability to execute well interventions for data acquistion at higher temperatures offers the potential for empirical studies that compare the status and integrity of the wellbore completion in thermal and cooled conditions.

Evaluation Method of the Vertical Well Hydraulic Fracturing Effect Based on Production Data

Hydraulic fracturing technology has become a key technology for the development of low-permeability/tight oil and gas reservoirs. The evaluation on the postfracturing effect is imperative to the formulation and implementation of the fracturing and development plan. Based on the characteristics of the flow in fracture network after a large-scale hydraulic fracturing, a numerical method for evaluating the effect of fracturing in vertical well was established. This study conducts postfracturing effect evaluations to block C Oilfield’s wells that underwent conventional fracturing and volumetric fracturing, respectively, proposes the definition of fracture network conductivity and its relationship with cumulative production, and analyzes the fracturing construction parameters. The results suggest that the conventional fracturing can only form a single fracture instead of a stimulated reservoir volume (SRV) region. However, the volumetric fracturing transformation can form a complex fracture network system and SRV region and meanwhile bring obvious increase in the production. The effective time lasts for a longer period, and the increase of average daily oil is 2.2 times more than that of conventional fracturing. Additionally, with the progress of the production, the SRV area within the core region of the volume transformation gradually decreased from 6664.84 m2 to 4414.45 m2; the SRV area of the outer region decreased from 7913.5 m2 to 5391.3 m2. As the progress develops, the equivalent permeability and the area of the fracture gradually decrease as the fracturing effect gradually weakens, and so does the conductivity of the network decreasing exponentially; a good correlation is observed between the conductivity of the fracture network, the cumulative production, and fracturing construction parameters, which can serve as the evaluation parameters for the fracturing effects and the basis for fracturing productivity prediction and provide a guidance for fracturing optimization design.

Production Analysis for Fractured Vertical Well in Coal Seam Reservoirs with Stimulated Reservoir Volume

The development and utilization of coalbed methane is of great significance to reduce carbon dioxide emission. Through the research, this paper presents a fast analytical solution method for the productivity of coalbed methane reservoir with finite-conductivity fractured well and stimulated reservoir volume region. Based on the dual-porosity flowing mechanism, combined with the Langmuir adsorb equation, Fick diffusion law, and Darcy law, a mathematical model considering diffusion in matrix and transport in natural fracture system is established, using spherical matrix to describe the transient steady-state sorption, and using cubic matrix to describe the pseudosteady-state sorption. Then, combined with the inner system and outer system, the analytical solution was obtained. Furthermore, the accuracy of the solution was validated against a numerical simulation. According to the Duhamel principle, the effect of wellbore storage and skin factor was got. Due to the SRV region, the linear flow and radial flow will appear before the pressure wave reach the outer region. And then, based on the pressure analysis result, we will have made the sensitivity analysis with different influence parameter. The result reveals that storage coefficient and conductivity factor mainly influence the early time; the permeability ratio and dimensionless SRV region radius mainly influence the property of SRV region. Finally, the analytical solution of the new model was applied to field history match. This model takes into account the adsorption and desorption characteristics of coalbed methane, as well as the SRV zones generated during fracturing. The calculation speed of the new model is increased while the calculation accuracy is retained, and the intensity of software application is reached. The model achieves the purpose of rapid evaluation and accurate prediction of gas well productivity and obtains a set of productivity evaluation method suitable for coalbed methane reservoir with fractured vertical well, which provides a basis for the development and productivity evaluation of coalbed methane reservoir in domestic and international cooperation.