Method and Application of Reducing Pressure and Increasing Production in Nanometer Porous Coal Seam

Objectives: In order to deeply analyze the feasibility of reducing pressure and increasing production of coalbed methane wells in nano-porous coal seams and clarify the principle of well selection. Methods: The sensitivity of bottom hole flowing pressure to coalbed methane production is analyzed by establishing productivity equation in stable production period of coalbed methane wells. Combined with the numerical simulation method, the drainage and production effect of L-1 well in the Block A is simulated after reducing the flowing pressure at the bottom of the well. Results: The results show that for CBM wells that have been put into production, the effect of increasing the production can be achieved by reducing the bottom hole flowing pressure, and when the bottom hole flowing pressure is large, reducing the bottom hole flowing pressure can obtain a larger increase in gas production. The cumulative gas production of Well L-1 can be increased by 110x104m3 compared with the previous measures, and the increase rate can reach 85%. Conclusion: Combining with the pressure-reducing and increasing production wells in the Block A, the applicable conditions for pressure-dropping and increasing production to increase the production of CBM wells are proposed, that is, continuous and stable drainage and production, and there is a certain height of liquid column between the moving liquid level and the coal roof before operation.

Gas Deliverability Monitoring and Reserves Quantification without Shut-In the Well: Application of Coupled Material Balance - Nodal Analysis Approach in Main Zone of Tunu Field, Mahakam

The classical Material Balance (P/Z) plot requires fully shut-in built-up reservoir pressure (Pr) for its calculation by generating static Pr as a function of cumulative gas production (Gp). Shut-in the well only for Pr data acquisition is impractical and creates several issues such as risk of production loss and production disturbance. Mattar & McNeil (1997) introduced Flowing Material Balance approach for gas deliverability monitoring and reserves estimation based on surface well flowing parameter by creating parallel line through the initial Pr to estimate Initial-Gas-In-Place (IGIP). The method is practical for qualitative purpose, but any dynamic behavior of the well will be challenging. Improved model is presented, a Coupled Material Balance - Nodal Analysis approach for gas deliverability monitoring and reserves quantification of connected gas in place volume (CGIP). Initial Pr as a known variable then extended by the decline of Pr as a function of Gp and improved by performing “flowing mode” Nodal Analysis, converting bottom hole flowing pressure from wellhead flowing pressure to determine estimated Pr. Pr uncertainty and its depletion could be identified by sensitivity analysis, such as inflow productivity and water encroachment evolution. This approach has been applied for well T-32 of Tunu field, a mature field in Mahakam, to perform as single-reservoir gas deliverability monitoring by using only flowing parameter data. The “flowing” mode of Pr estimation with actual Gp, gives good performance of CGIP estimation without any shut-in activities, since this well is one of the big gas producer. This model also handled the dynamic activities of operation: well movement, production curtailment and improvement. The unknown variable of continuous water encroachment is also handled by wellbore temperature model which justified with actual data. This improved model could be considered as an alternative approach for gas reserves quantification and gives advantage for production strategy.

Effect of the Angle between Hydraulic Fracture and Natural Fracture on Shale Gas Seepage

Fracturing technology is an effective measure to exploit shale gas and the fractures improve the seepage ability of shale reservoir after fracturing. In this paper, taking Chang 7 of Yanchang Formation as the study area, a double porosity seepage model considering natural fracture was established and it was solved by finite element method of COMSOL5.5; then, shale gas seepage was analyzed under different angles between hydraulic fracture and natural fracture finally. Meanwhile, angles between hydraulic fracture and natural fracture were optimized by analyzing both the reservoir pressure distribution and bottom hole flowing pressure. Also, a permeability experiment with liquid was conducted to verify the accuracy of the numerical simulation result. Both numerical simulation and permeability measurement experiment get a uniform result that the optimal angle between hydraulic fracture and natural fracture is 90°. Permeability is the highest, shale gas seepage rate is the fastest, bottom hole flowing pressure is the highest, and also it is beneficial to the desorption of adsorbed gas in the matrix system and then effectively supplements reservoir pressure and bottom hole flowing pressure. The research results will provide some theoretical guidance for fracturing design.

Calculation Method for Inflow Performance Relationship in Sucker Rod Pump Wells Based on Real-Time Monitoring Dynamometer Card

Based on the informatization and intelligent construction of an oilfield, this paper proposes a new method for calculating inflow performance relationship in sucker rod pump wells, which solves the limitations of current IPR curve calculation method in practical application. By analyzing the forming principle of the dynamometer card, the plate of abnormal dynamometer card is created innovatively, and the recognition model of abnormal dynamometer card based on “feature recognition” is established to ensure the accuracy of the dynamometer card. By analyzing the curvature of each point on the curve of downhole pump dynamometer card, the opening and closing points of standing valve and traveling valve are determined, and the models for calculating fluid production and bottom hole flowing pressure are established to obtain the data of fluid production and bottom hole flowing pressure of sucker rod pump wells. Finally, a calculation model of inflow performance relationship fitted with the calculated fluid production and bottom hole flowing pressure data based on genetic algorithm is established to realize calculation of oil well inflow performance relationship curve. The field application and analysis results show that the inflow performance relationship curve calculated by the model in this paper fits well with the measured data points, indicating that the calculation model has high accuracy and can provide theoretical and technical support for the field. Moreover, the real-time acquisition of dynamometer cards can provide real-time data source for this method, improve the timeliness of oil well production analysis, and help to reduce the production management costs and improve the production efficiency and benefit.

Role of Gas Viscosity for Shale Gas Percolation

Viscosity is an important index to evaluate gas flowability. In this paper, a double-porosity model considering the effect of pressure on gas viscosity was established to study shale gas percolation through reservoir pressure, gas velocity, and bottom hole flowing pressure. The experimental results show that when pressure affects gas viscosity, shale gas viscosity decreases, which increases the percolation velocity and pressure drop velocity of the free state shale gas in matrix and fracture systems. And it is conducive to the desorption of adsorbed shale gas and effectively supplemented the bottom hole flowing pressure with the pressure wave propagation range and velocity increasing, so that the rate of pressure drop at the bottom of the well slows down, which makes the time that bottom hole flowing pressure reaches stability shortened. Therefore, the gas viscosity should be fully considered when studying the reservoir gas percolation.

Improved capacitance model considering bottom-hole flowing pressure and interference between oil wells

With the continuous production of oil wells, the reservoir properties, such as permeability and porosity, are changing accordingly, and the reservoir heterogeneity is also enhanced. This development is vulnerable to the problem of the one-way advance of injected water and low efficiency of water flooding. The interwell connectivity between injection and production wells controls the flow capacity of the subsurface fluid. Therefore, the analysis of interwell connectivity helps to identify the flow direction of injected water, which is of great significance for guiding the profile control and water plugging in the later stage of the oilfield. In this study, based on the principle of mass conservation, a capacitance model considering the bottom-hole flowing pressure was established and solved by using the production dynamic data of injection–production wells. Then, the validity of the capacitance model was verified by numerical simulation, and the influences of well spacing, compression coefficient, frequent switching wells, injection speed, and bottom-hole flowing pressure on interwell connectivity were eliminated. Finally, a practical mine technique for inversion of connectivity between wells using dynamic data was developed. The advantage of this model is that the production dynamic data used in the modeling process are easy to obtain. It overcomes the shortcomings of previous models and has a wider range of applications. It can provide a theoretical basis for the formulation of profile control and water-plugging schemes in the high-water-cut period.