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.

Flowing Material Balance and Rate-Transient Analysis of Horizontal Wells in Under-Saturated Coal Seam Gas Reservoirs: A Case Study from the Qinshui Basin, China

Two phase flow and horizontal well completion pose additional challenges for rate-transient analysis (RTA) techniques in under-saturated coal seam gas (CSG) reservoirs. To better obtain reservoir parameters, a practical workflow for the two phase RTA technique is presented to extract reservoir information by the analysis of production data of a horizontal well in an under-saturated CSG reservoir. This workflow includes a flowing material balance (FMB) technique and an improved form of two phase (water + gas) RTA. At production stage of a horizontal well in under-saturated CSG reservoirs, a FMB technique was developed to extract original water in-place (OWIP) and horizontal permeability. This FMB technique involves the application of an appropriate productivity equation representing the relative position of the horizontal well in the drainage area. Then, two phase (water + gas) RTA of a horizontal well was also investigated by introducing the concept of the area of influence (AI), which enables the calculation of the water saturation during the transient formation linear flow. Finally, simulation and field examples are presented to validate and demonstrate the application of the proposed techniques. Simulation results indicate that the proposed FMB technique accurately predicts OWIP and coal permeability when an appropriate productivity equation is selected. The field application of the proposed methods is demonstrated by analysis of production data of a horizontal CSG well in the Qinshui Basin, China.

Tight Gas Reservoir Dynamic Reserve Calculation with Modified Flowing Material Balance Method

The determination of dynamic reserves of gas well is an important basis for rational production allocation and development of a single well. The commonly used flow material balance method (FMB method) uses the slope of the curve of wellhead pressure and cumulative production after stable production of gas well to replace the slope of the curve of average formation pressure and cumulative production to calculate the controlled reserves of single well. However, based on the theoretical calculation, the FMB method ignores the change of natural gas compression coefficient, viscosity and deviation coefficient in the production process. After considering these changes, the slope of the curve of the relationship between bottom hole pressure and cumulative production and the slope of the curve of the relationship between average formation pressure and cumulative production are not equal. In order to solve this problem, the influence of pressure on each parameter is considered, and the equation of modified flowing material balance method is derived. The application of Yan'an gas field in Ordos Basin shows that: compared with the results of the material balance method, the result of the flow material balance method is smaller, and the maximum error is 58.816%. The consequence of the modified mobile material balance method is more accurate, and the average error is 2.114%, which has good applicability. This study provides technical support for an accurate evaluation of dynamic reserves of tight gas wells in Yan'an gas field, and has important guiding significance for economic and efficient development of gas reservoir.

Application of DFIT-FBA Tests Performed at Multiple Points in a Horizontal Well for Advanced Treatment Stage Design and Reservoir Characterization

The DFIT flowback analysis (DFIT-FBA) method, recently developed by the authors, is a new approach for obtaining minimum in-situ stress, reservoir pressure, and well productivity index estimates in a fraction of the time required by conventional DFITs. The goal of this study is to demonstrate the application of DFIT-FBA to hydraulic fracturing design and reservoir characterization by performing tests at multiple points along a horizontal well completed in an unconventional reservoir. Furthermore, new corrections are introduced to the DFIT-FBA method to account for perforation friction, tortuosity, and wellbore unloading during the flowback stage of the test. The time and cost efficiency associated with the DFIT-FBA method provides an opportunity to conduct multiple field tests without delaying the completion program. Several trials of the new method were performed for this study. These trials demonstrate application of the DFIT-FBA for testing multiple points along the lateral of a horizontal well (toe stage and additional clusters). The operational procedure for each DFIT-FBA test consists of two steps: 1) injection to initiate and propagate a mini hydraulic fracture and 2) flowback of the injected fluid on surface using a variable choke setting on the wellhead. Rate transient analysis methods are then applied to the flowback data to identify flow regimes and estimate closure and reservoir pressure. Flowing material balance analysis is used to estimate the well productivity index for studied reservoir intervals. Minimum in-situ stress, pore pressure and well productivity index estimates were successfully obtained for all the field trials and validated by comparison against a conventional DFIT. The new corrections for friction and wellbore unloading improved the accuracy of the closure and reservoir pressures by 4%. Furthermore, the results of flowing material balance analysis show that wellbore unloading might cause significant over-estimation of the well productivity index. Considerable variation in well productivity index was observed from the toe stage to the heel stage (along the lateral) for the studied well. This variation has significant implications for hydraulic fracture design optimization, particularly treatment pressures and volumes.

An Effective Interface Tracking Method for Simulating the Extrudate Swell Phenomenon

The extrudate swell, i.e., the geometrical modifications that take place when the flowing material leaves the confined flow inside a channel and moves freely without the restrictions that are promoted by the walls, is a relevant phenomenon in several polymer processing techniques. For instance, in profile extrusion, the extrudate cross-section is subjected to a number of distortions that are motivated by the swell, which are very difficult to anticipate, especially for complex geometries. As happens in many industrial processes, numerical modelling might provide useful information to support design tasks, i.e., to allow for identifying the best strategy to compensate the changes promoted by the extrudate swell. This study reports the development of an improved interface tracking algorithm that employs the least-squares volume-to-point interpolation method for the grid movement. The formulation is enriched further with the consistent second-order time-accurate non-iterative Pressure-Implicit with Splitting of Operators (PISO) algorithm, which allows for efficiently simulating free-surface flows. The accuracy and robustness of the proposed solver is illustrated through the simulation of the steady planar and asymmetric extrudate swell flows of Newtonian fluids. The role of inertia on the extrudate swell is studied, and the results that are obtained with the newly improved solver show good agreement with reference data that are found in the scientific literature.

Physics and Modeling of Various Hazardous Landslides

In 2014, the Varnes classification system for landslides was updated. Complex landslides can still be a problem to classify as the classification does not include the flow type in the hydrodynamical sense. Three examples of Icelandic landslides are presented and later used as case studies in order to demonstrate the methods suggested to analyze the flow. The methods are based on the different physical properties of the flow types of the slides. Three different flow types are presented, named type (i), (ii), and (iii). Types (i) and (ii) do not include turbulent flows and their flow paths are sometimes independent of the velocity. Type (iii) include high velocity flows; they are treated with the translator wave theory, where a new type of a slope factor is used. It allows the slide to stop when the slope has flattened out to the value that corresponds to the stable slope property of the flowing material. The type studies are for a fast slide of this type, also a large slip circle slide that turns into a fast-flowing slide farther down the path and finally a large slide running so fast that it can run for a kilometer on flat land where it stops with a steep front.

Average Fracture Compressibility from Flowback Data

Summary We propose a novel method for estimating average fracture compressibility cf¯ during flowback process and apply it to flowback data from 10 multifractured horizontal wells completed in Woodford (WF) and Meramec (MM) formations. We conduct complementary diagnostic flow-regime analyses and calculate cf¯ by combining a flowing-material-balance (FMB) equation with pressure-normalized-rate (PNR)-decline analysis. Flowback data of these wells show up to 2 weeks of single-phase water production followed by hydrocarbon breakthrough. Plots of water-rate-normalized pressure and its derivative show pronounced unit slopes, suggesting boundary-dominated flow (BDF) of water in fractures during single-phase flow. Water PNR decline curves follow a harmonic trend during single-phase- and multiphase-flow periods. Ultimate water production from the forecasted harmonic trend gives an estimate of initial fracture volume. The cf¯ estimates for these wells are verified by comparing them with the ones from the Aguilera (1999) type curves for natural fractures and experimental data. The results show that our cf¯ estimates (4 to 22×10−5 psi−1) are close to the lower limit of the values estimated by previous studies, which can be explained by the presence of proppants in hydraulic fractures.