Biot’s theory of poroelasticity has gained new prominence in rock mechanics to understand the hydro-mechanical (H-M) response of fluid flow and deformation in tunneling in deep saturated ground. Numerically, explicit coupling technique has been widely used for simulating this coupled interaction. However, the technique is conditionally stable and requires small time steps, making it inefficient for simulating large-scale H-M problems. To improve the efficiency, the unconditionally stable alternating direction explicit (ADE) scheme could be used to solve the flow problem. The standard ADE scheme, however, is only moderately accurate and is restricted to uniform grids and plane strain problems. Thus, it is impractical for large-scale domains and inapplicable for axisymmetric problems. This paper aims to remove these drawbacks by developing a novel high-order ADE scheme capable of solving the flow problem in an axisymmetric non-uniform grid. The new scheme is derived by performing a fourth-order finite difference approximation for the spatial derivatives of the axisymmetric fluid-diffusion equation in a non-uniform grid configuration. The implicit Crank-Nicolson technique is then applied to the resulting approximation, and the subsequent equation is split into two alternating direction sweeps, giving rise to a new high-order axisymmetric ADE scheme. The pore pressure solutions from the new scheme are then sequentially coupled with an existing geomechanical simulator in the computer code Fast Lagrangian Analysis of Continua (FLAC). This coupling procedure is called the sequentially-explicit coupling technique based on the fourth-order axisymmetric ADE scheme or SEA-4-AXI. When applied for simulating an advancing tunnel in deep saturated ground, SEA-4-AXI reduces computer runtime up to 42% that of FLAC’s basic scheme without numerical instability while also producing high numerical accuracy with average differences of 0.6-1.8% for pore pressure and displacement.
Biot’s theory of poroelasticity (Biot, 1941) has gained new prominence in rock mechanics to understand the coupled response of fluid flow and deformation in deformable porous media (i.e., soils and rocks). Consolidation and subsidence induced by fluid extraction from underground formations are the most common examples of this coupled hydro-mechanical (H-M) interaction. In these examples, the transient fluid flow affects deformation in the ground and vice versa (Wang, 2000; Gutierrez and Lewis, 2002; Neuzil, 2003). Thus, consideration of this H-M interaction is essential for the safe design of underground structures such as deep tunnel in saturated ground.
Drill and blast is the excavation method adopted to remove overburden material at the open pit coal mine of PT Buma Job Site Lati. Recently, the company applied deep hole drilling for blasting with double rods to reach the depth of 10-18 m. The main explosive was an emulsion explosive with target explosive consumption of 0.23 kg/m3. The blast hole was not fully charged but vertically decoupled using air decks at the middle and bottom of each blasting hole. Blasted rocks were then measured by digital photograph, and the size of P80 was found to range from 200 to 800 mm. The evaluation results indicate there is close relationship between the explosive consumption and the fragment size as well as the digging time. The air deck technique adopted in this study has been giving good results in terms of fragmentation size and explosive consumption.
In mining operations, drilling and blasting with a deep hole is a preferred method to reduce lost production time caused by the delays in blasting, to increase blasting inventory, and to minimize the number of drill pads so the drilling deviation can be minimized as well. Recently, PT BUMA Job Site Lati (called BUMA from now on) applied drilling for blasting operations with double rods to reach the depth of 10-18 m. Consequently, explosive consumption was high in the lower part of the blast hole, then an air deck was used to distribute the explosive along the blast hole. Another benefit of the air deck was that it cut the waiting time of the on-site sensitized explosive expansion to accommodate gassing.
In this study, the performance of blasting operation using the air deck is evaluated in terms of fragmentation. This study aims to check the effectiveness of using an air deck with the productivity target at the particular mine and to develop a blasting-fragmentation model that can be used to predict the size of the fragmented rock.
2. Literature Review
The air deck method is well-known in blasting operations to improve the quality of the blasting results. In the early 1940s, Russian scientists first came up with the idea of using an air gap between explosive columns. This method reduced explosive consumption in blasting activity. Melnikov et al. (1979) mentioned that an air deck can act as an energy accumulator. Marchenko (1982) found that pressure in an air deck would expand micro fractures that were previously generated by the main shock wave during blasting. Pompanna and Chikkareddy (1993) concluded that the presence of an air gap in the blast hole can reduce ground vibration and back break at the Kudrremukh iron mines. Jhanwar et al. (1996) revealed that the mechanism of air deck can reduce 25-30% of explosive consumption. Chiapppeta (2004) conducted experiments in the field and found that the air deck technique could remove the sub-drill which in turn reduced the explosive consumption by 16-25%, decreased vibration due to blasting by 33%, and improved fragmentation by 25%.
Utilization of an air deck will increase the fracture network due to the secondary shock waves formed as the result of wave reflection in the air gap. The fracture degree increases as a result of secondary shock waves as the duration of the shock wave effect on the rock mass around the blast hole becomes longer. The pressure reflections from the upper and lower explosive columns will collide in the middle of the air deck and is expected to interact with the surrounding rock mass to form additional radial fractures (Moxon et al., 1993; Zhang, 2016; see Fig.1). Air deck methods have been used in some open pit mines to reduce the consumption of explosive and to improve fragmentation (Chiapetta, 2004).
Tunnel collapse in weak rock masses occurs when the support pressure given by the installed support system is not adequate to sustain the weight of broken rock resulting from the excavation. Further, installation of support system will encounter great difficulty when the maximum allowable limit of strain before setting up the support is exceeded. This paper presents the results of numerical simulations in computer code FLAC to integrate the use of ground reaction curve and equilibrium strain approach for designing tunnel support system in a non-circular excavation. The equilibrium strain is used as one of the design tools because the final radial deformation of a supported tunnel occurs at the equilibrium between the support and the deforming ground, not at the time of support installation. The approach is demonstrated on a large cross-section road tunnel that is excavated through weak rock masses with varying qualities. Results from the FLAC model show that when the time to install support system is correctly estimated at the equilibrium strain εeq of 1%, the amount of vertical deformation and the extent of the plastic zone around the tunnel decrease significantly. This correct estimation is made possible with the help from the ground reaction curve (GRC). Moreover, as shown by the support capacity diagrams, the induced bending moment, axial and shear loads in the tunnel lining are well inside the strength envelopes of the support system with factor of safety > 1.5. Results from this research indicate that the integrated use of GRC and equilibrium strain approach can be used as a tool to achieve a reliable tunnel support design.
Designing a tunnel support system in weak rock masses must cope with the estimation of support pressure that is needed to stabilize the tunnel face and the newly-opened room behind the face. In this situation, collapse of the opening occurs when the support pressure given by the installed support system is not adequate to sustain the weight of broken rock resulting from the excavation. In particular, installation of support system will encounter great difficulty when the maximum allowable limit of strain before setting up the support is exceeded.
The so-called convergence-confinement method (CCM) has been a standard practice for evaluating the displacement behavior of a tunnel and to determine the required support pressure to control the convergence of the tunnel wall (Carranza-Torres and Fairhurst, 2000; Vlachopoulos and Diederichs, 2009; Prassetyo, 2017; Prassetyo and Gutierrez, 2018). The CCM consists of the ground reaction curve (GRC), the support reaction curve (SRC), and the longitudinal displacement curve (LDP). The GRC represents the relationship between the increasing radial displacement of the tunnel wall ur and the decreasing internal support pressure pi. The SRC represents the relationship between the increasing support pressure ps and the increasing radial displacement of the support us. The last component, the LDP, represents the radial displacement occurring along the longitudinal axis of the unsupported tunnel.
Barton’s joint model is the most realistic model for predicting the nonlinear shear behavior of rock joints. This capability comes from the inclusion of a joint surface roughness parameter called the joint roughness coefficient (JRC) that is mobilized under shearing. Recently, a linearized implementation of Barton’s model has been done to obtain the mobilized equivalent Mohr-Coulomb (M-C) parameters that account for generation and reduction of JRC as a function of shear displacement ∆u. These equivalent parameters will allow the linear M-C model to capture nonlinearity in the shear behavior of rock joints. In the linearized Barton’s model, the pre- and post-peak joint shear stiffness also contains mobilized JRC that is expressed as hyperbolic and logarithmic functions of ∆u, respectively. This paper further explores the capability of the linearized Barton model to predict the shear behavior of rock joints. The model is verified against results from the experimental and numerical direct shear test on joint planes from various rock types. The verification shows that the linearized Barton’s model can capture the nonlinearity in the shear stress-displacement and in the dilation-induced shear displacement behaviors of rock joints under variations normal stress and JRC values. In the future, the linearized Barton’s model has the potential to be applied in computer codes for fractured rock modeling. By implementing this model, neither the simplicity of the linear M-C model nor the advanced capability of the nonlinear Barton’s model is lost.
In a fractured rock mass, the shear behavior of rock joints is particularly important because it dominantly controls the deformability, strength, and hence the stability of the rock mass. Block sliding from a slope or block falling in an underground excavation are examples of joint shear behavior that is not only controlled by the shear strength of the particular joint but also by its dilation (Goodman, 1976; Barton, 1982). The dilation is caused by the mobilization of joint surface roughness, causing a nonlinearity in the shear behavior of rock joints in the form of strain hardening and strain softening under shearing.
Hartono, A. D. (Kyushu University) | Hakiki, F. (King Abdullah University of Science and Technology) | Syihab, Z. (Institut Teknologi Bandung) | Ambia, F. (SKK Migas) | Yasutra, A. (Institut Teknologi Bandung) | Sutopo, S. (Institut Teknologi Bandung) | Efendi, M. (Pertamina Upstream Technology Center) | Sitompul, V. (Pertamina Upstream Technology Center) | Primasari, I. (Pertamina Upstream Technology Center) | Apriandi, R. (Pertamina Upstream Technology Center)
EOR preliminary analysis is pivotal to be performed at early stage of assessment in order to elucidate EOR feasibility. This study proposes an in-depth analysis toolkit for EOR preliminary evaluation. The toolkit incorporates EOR screening, predictive, economic, risk analysis and optimisation modules. The screening module introduces algorithms which assimilates statistical and engineering notions into consideration. The United States Department of Energy (U.S. DOE) predictive models were implemented in the predictive module. The economic module is available to assess project attractiveness, while Monte Carlo Simulation is applied to quantify risk and uncertainty of the evaluated project. Optimization scenario of EOR practice can be evaluated using the optimisation module, in which stochastic methods of Genetic Algorithms (GA), Particle Swarm Optimization (PSO) and Evolutionary Strategy (ES) were applied in the algorithms. The modules were combined into an integrated package of EOR preliminary assessment. Finally, we utilised the toolkit to evaluate several Indonesian oil fields for EOR evaluation (past projects) and feasibility (future projects). The attempt was able to update the previous consideration regarding EOR attractiveness and open new opportunity for EOR implementation in Indonesia.
Hakiki, Farizal (King Abdullah Univesity of Science and Technology) | Wibowo, Aris T. (Pertamina EP) | Rahmawati, Silvya D. (Institut Teknologi Bandung) | Yasutra, Amega (Institut Teknologi Bandung) | Sukarno, Pudjo (Institut Teknologi Bandung)
One of the major concerns in a multi-layer system is that interlayer cross-flow may occur if reservoir fluids are produced from commingled layers that have unequal initial pressures. Reservoir would commonly have bigger average reservoir pressure (pore fluid pressure) as it goes deeper. The phenomenon is, however, not followed by the reservoir productivity or injectivity. The existence of reservoir with quite low average-pressure and high injectivity would tend experiencing the cross-flow problem. It is a phenomenon of fluid from bottom layer flowing into upper layer. It would strict upper-layer fluid to flow into wellbore. It is as if there is an injection treatment from bottom layer. The study deploys productivity index an approach parameter taking into account of cross-flow problem instead of injectivity index since it is a production well. The analytical study is to model the reservoir multilayer by addressing to avoid cross-flow problem. The analytical model employed hypothetical and real field data to test it. The scope of this study are: (a) Develop mathematical-based solution to determine the production rate from each layer; (b) Assess different scenarios to optimize production rate, those are: pump setting depth and performance of in-situ choke (ISC) installation. The ISC is acting as an inflow control device (ICD) alike that help to reduce cross-flow occurrence. This study employed macro program to write the code and develop the interface. Fast iterative procedure happens on solving the analytical model. Comparison results recognized that the mathematical-based solution shows a good agreement with the commercial software derived results.
Aslam, B. M. (Institut Teknologi Bandung) | Ulitha, D. (Institut Teknologi Bandung) | Swadesi, B. (Institut Teknologi Bandung) | Fauzi, I. (Institut Teknologi Bandung) | Marhaendrajana, T. (Institut Teknologi Bandung) | Purba, F. I. (Pertamina EP) | Wardhana, A. I. (Pertamina EP) | Buhari, A. (Pertamina EP) | Hakim, R. (Pertamina EP) | Hasibuan, R. (Pertamina EP)
Tanjung Field is a brown field which pressure has already depleted and been supported by waterflooding for over a decade. To improve production, surfactant injection, is being studied to be employed in the field. The main objective of this study is to identify parameters that affect oil production increase. History match of the pilot test was carried out to improve the reliability of the reservoir model, hence improving the prediction result of surfactant injection forecast.
History match of the pilot test has been carried out using CMG STARS commercial simulator by considering mechanism inferred from laboratory evaluation such as wettability alteration, surfactant retention, interfacial tension reduction and improvement of mobility control due to lower oil-surfactant emulsion viscosity. These parameters are initially perceived from laboratory result, upscaling and adjustment is applied to field model to further on do sensitivity study. Sensitivity analysis of every parameter is provided to better understand the effect of each mechanism that contributes to the oil incremental result.
Stratigraphically, Tanjung Structure has 7 productive zones: Zone A, B, C, D, E, F and P. Reservoir Zone A has total estimated reserve of 193,732 MMSTB, with recovery factor of 16.3%. The zone consists of conglomerate sandstones with porosity of 21% and permeability ranging from 10 to 100 mD. The field produces light oil within 40 °API, 30% wax content and 1.14 cP of viscosity. T-119 is the well chosen to be injected due to its structural position that ease flow by gravity force to producer wells.
Forecast simulation based on coreflood result has been conducted for pilot test. However, the result was very pessimistic in predicting incremental oil gain and breakthrough time after compared to pilot result. An attempt to history match the surfactant flood pilot is presented by considering phenomena that is not included in the forecast based on additional lab and field data.
Bachtiar, A. W. (PT. Pertamina EP) | Purba, F. I. (PT. Pertamina EP) | Dusyanto, E. D. (PT. Pertamina EP) | Mucharam, L. (Institut Teknologi Bandung) | Swadesi, B. (Institut Teknologi Bandung) | Santoso, R. K. (Institut Teknologi Bandung) | Fauzi, I. (Institut Teknologi Bandung) | Hidayat, M. (Institut Teknologi Bandung) | Aslam, B. M. (Institut Teknologi Bandung) | Dzulkhairi, H. (Institut Teknologi Bandung) | Surya, A. (Institut Teknologi Bandung) | Marhaendrajana, T. (Institut Teknologi Bandung)
Injectivity is a critical issue in polymer injection since it determines the success of polymer to displace and sweep oil in the reservoir. Polymer has shear rate and temperature-dependence viscosity which is substantially different behaviorfrom water. Any calculation related to injection performance should consider this behavior. Injector should be organized to achieve the desired injection rate without any issue. The easiest approach to design the optimum injector is using IPR-TPR method. Therefore, in this paper, we develop Non-Newtonian IPR-TPR method to achieve optimum completion design of injector. The IPR equation is built using modified Darcy equation for Non-Newtonian fluid. The TPR equation is developed using
We used case study of T-048 – T-012 injector-producer in Tanjung Field Zone-C, Indonesia with 500 and 2,000 ppm HPAM polymer. Simulation results show that there exists changing process from shear thinning to Newtonian along the tubing because of temperature and injection velocity while only Newtonian behavior occurs in near wellbore for 500 ppm injection case. Smaller tubing OD produces higher effective injection rate than the bigger one. The 2,000 ppm polymer cannot enter the reservoir due to bottomhole pressure reaches the fracture presure.Finally, smaller tubing OD (below 2.875 in) is suitable in Tanjung Field Zone-C for 500 ppm polymer injection. 2,000 ppm polymer cannot be deployed and needed further evaluation.
Wettability becomes a crucial parameter in understanding the reservoir rock behavior due to its effect on characterizing the distribution of fluid saturation, estimation of primary oil recovery, and certainly to determine the IOR/EOR application plans. However, many practitioners in core laboratory analysis use inappropriate fluids (synthetic oil) in measuring special core analysis (SCAL), while the detail compositions of fluid in reservoir condition can strongly influence the wettability value. As the consequences, the results of measurement give unmatched to the real reservoir condition. This paper dedicates a case in carbonate reservoir to estimate in-situ reservoir wettability and capillary pressure by using wireline pressure test data and conventional log while the core data analysis are un-trusted to be implemented.
Two well cases are used in this study from a carbonate reservoir field located in the North East Java Basin area. Relative permeability, capillary pressure, and electrical property obtained from the core measurement of TB reservoir shows that the wettability of TB Reservoir is water wet. The interpretation of in-situ wettability using reservoir pressure test data suggests that the wettability of rock is weakly oil wet. This study also re-construct the capillary pressure which is appropriate with in-situ wettability.
Regarding to this case, an integrated analysis of conventional log and wireline formation testing data are strongly needed. At first, Free Water Level (FWL) and Oil Water Contact (OWC) are determined by integrating formation pressure test, flow test, and well log data (especially for resistivity log) which can also be used to define the reservoir wettability. Then, the vertical water saturation is interpreted by simple Archie’s equation with a and m parameters are obtained from Pickett Plot and n is generated from Al-Hilali’s method and Krygowski and Cluff’s method. By plotting and interpreting formation pressure data versus depth and vertical fluid saturation from electrical log respectively, a new capillary pressure curve model and wettability are established.
Properties of rock mass vary and an exact value of one of the properties at any given location cannot be predicted. On the other hand, in applying some classical methods of structure stability analyses, only one value of certain parameter must be input to the formulas or even the computer codes. Stability of the structure is evaluated by comparing the capacity (strength or resisting force) of the structure and the demand (stress or disturbing force) and expressed in term of Factor of Safety (FoS). The FoS calculated by this deterministic approach obviously has limitation for assuring the stability of structure.
The rock mass uncertainties can be dealt with by taking into account statistical distributions of the parameters in the FoS calculation or by developing empirical design guidelines or curves based on a particular regression techniques on case histories of stable and unstable structures with particular design parameters and properties. This paper gives some examples illustrating approaches for dealing with uncertainties in the rock mass.
Design and construction in rock require processes and procedures that are in many ways different from other design and construction projects, because the main construction material is the rock mass itself rather than an engineered material. The rock mass properties do not have a single fixed value but may assume any number of values at any given location. It is then obvious that the classical approach of Factor of Safety (FoS) where the calculations are based on one value of a certain parameter, is unable to fully assure that a structure with FoS greater than 1.0 will be stable.
Two approaches can be utilised in dealing with the rock mass properties uncertainties. First, the FoS calculation is conducted by taking into consideration all possible values of rock mass properties. In practice, the values can be represented by the statistical mean and the standard of deviation of the parameters which depend on their statistical distribution functions. The calculated FoS then has also mean value and standard of deviation. Probability of having a particular value of FoS can also be calculated. Secondly, stable and unstable structures case histories can be collected and for practical reasons, the main data that must be recorded for each structure are geometry, strength, stress, and stability condition. Curve separating stable and unstable case histories can be constructed by using regression techniques. In addition, iso-probability of stable (or failure) curves can also be plotted.