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Abstract Unconventional oil and gas reservoirs are being explored significantly around the globe nowadays. The economical production of hydrocarbons from these unconventional oil and gas reservoirs like CBM requires very advanced and cost effective technologies. Hydraulic fracturing is such a technology which is being used in the oil and gas industry for many decades to create highly conductive channels in the formations having very low permeability values. Multistage hydraulic fracturing has been proved to be a great achievement in oil and gas industry to enhance the production from unconventional reservoirs. An effective hydraulic fracturing planning & execution is a key to achieve the expected results in terms of production from unconventional reservoirs such as tight gas, shale gas, coal bed methane or other very low permeability reservoirs. Unconventional reservoirs such as Shale & CBM require large scale hydraulic fracturing operations, where multiple frac fleets, wire-line units, coiled tubing units; work-over rigs & ancillary services are mobilized. A scheduling software based project management approach was followed at CBM Raniganj for planning & modeling of operations. This paper aims to study how the operational resource deployed in Raniganj field for hydraulic fracturing was optimized in terms of time, cost & load for fracturing operations. The approach of modeling & planning the hydraulic fracturing operations is based on project management & scheduling software. Assumptions were finalized based on experience. The loopholes, possible schedule slippages and other deterrents which could cause a lag in the hydro fracturing campaign aimed to pump over 1,600 frac jobs in CBM Raniganj field, over a period of 30 rig months, were identified clearly. The scope, time, budget & quality standards were clearly defined and a schedule was prepared with the help of the scheduling software to run the fleets in a clockwork manner. Activities like perforation, Acidizing, data fracturing, main fracturing, flowback, sand plug and finally sand cleanout were defined as series & simultaneous operation.
Abstract Raniganj field in West Bengal is the largest producing coal bed methane reservoir in India, belonging to the Gondwana Super Group. Block RG (East)-CBM-2001/1 is located in the eastern-most part of Raniganj coalfield. The block was awarded to Essar Oil Limited under the CBM Round I of the Government of India in 1997. More than 1200 hydraulic fracturing jobs have been carried out since then. Fracturing treatment plans for each well in this block comprises of more than one hydraulic fracturing job since this coal-bed reservoir is made up of a number of laminated sequences of coal seams separated at variable distances. Due to a very strong heterogeneity between these seams, it is essential to understand the behavior of fracture propagation in all of them individually. Fracture diagnostics involves analyzing the data before, during, and after a hydraulic fracture treatment to determine the shape and dimensions of both the created and propped fracture. Fracture diagnostic techniques can provide important data when entering a new area or a new formation. In most cases, however, fracture diagnostics is expensive, which limits its widespread use in industry. However, many researchers have come up with a much simpler and cost effective technique of predicting the fracture behavior based on the analysis of net pressure trend of the fracturing job. Analysis of fracturing treatment pressure behavior is an easy tool to gain some insight into the fracturing parameters and fracture propagation, and consequently, optimize the future fracturing treatments. The ever exhaustive fracturing database of Essar Oil Limited was taken into deliberation to study the fracturing treatments carried out in different seams and an attempt is made to correlate the efficacy of these treatments based on the diagnostic tools postulated by Nolte (1979) and Conway (1985). The study is been extended to correlate the fracturing behavior of each coal seam to the production history. Consequently, suggestions are provided to optimize the future fracturing treatments in order to increase the production index of each well. Formations like coal bed methane and other similar unconventionals are highly unpredictable when it comes to evaluating the accuracy of simulations carried out. This technique helps realize that each reservoir behaves differently and correlating different studies undertaken to study the particular reservoir will help engineers understand it better.
Abstract Pinpoint technology pioneers a specific technique wherein target zones are selectively perforated by pumping abrasive fluids through a specifically designed coiled-tubing (CT)-deployed bottomhole assembly (BHA) to perform abrasive jetted perforating. This provides an economical and efficient method of perforating, which is immediately followed by fracture stimulating the interval without removing the CT. This is achieved by pumping the fracturing fluid down the casing-CT annulus. The fractured zone is then isolated after the fracturing stage is complete by means of a sand plug, immediately followed by individually treating multiple additional zones in a similar fashion. This is all performed without having to pull the CT completely out of the well. With sand plugs being the primary mode of zonal isolation, an attempt should be made to achieve a proppant packoff using higher concentrations of sand in the final stages of each fracturing treatment (except the top one). This pinpoint stimulation method involves the synergistic integration of CT and fracture stimulation disciplines of well services. This paper highlights the lessons learned from both operational and engineering standpoints of CT applications during the process of executing a coalbed methane (CBM) fracturing campaign in the Raniganj field of West Bengal, India. The discussions within this paper focus on engineering best practices, optimization of resource utilization, increment of the number of treated zones per day, and reduction of non-productive time (NPT). This treatment technique provides an easy and economical method for achieving depth correlation. The small seam thickness of the CBM zones to be fractured requires a precise depth correlation technique to help ensure that the perforations are placed within the target seam. A mechanical casing collar locator (MCCL) tool is employed during this process, which helps correlate the CT depth to the wireline depth. This is why the success of this tool, to a major extent, depends on the accuracy of the wireline logs supplied by the well operator, to which the collar depths are correlated. This paper also discusses the optimization of this tool, which resulted in an increase to the tool life and reduction of downtime caused by unnecessary roundtrips of CT, consequently reducing total fatigue on the CT string. A prominent feature of this treatment method is the hydrajetting technique, which uses abrasive sand jetting to cut perforations through the casing, through the cement sheath, and farther into the formation. It provides a cleaner and more economical method of perforating compared to conventional perforating techniques. This can result in reduction of entry friction and larger perforation diameters, leading to enhanced communication to the reservoir and lowering of fracture initiation pressure. While perforating the CBM formation, several parameters were manipulated to augment the technical and operational efficiency of the entire process, which are discussed in this paper. Once the perforations are cut, acid is displaced down the CT to clean the cement remains and debris from the perforating. An inherent advantage of using CT in this process is acid being spotted directly into the perforations, causing a more effective cleaning of the perforation set, often characterized by reduction to treating pressure during fracturing stages. This paper discusses a case in which, during the execution of hydra jet perforating in deviated wells, one of the major challenges encountered was the inability to lift cutting sand from casing (post perforating) using forward circulation (pumped through CT and returns taken through the annulus). Ideally, during a hydrajetting process, cutting sand is circulated out of the wellbore once the cut is complete. However, in these highly deviated sections, because of the size of CT and casing used, there was insufficient annular velocity to lift cutting sand from the well. This issue was resolved using unconventional methods, which are also discussed in this paper.
Abstract Dewatering is required to remove water from the coal seams so that bottomhole pressure (BHP) is reduced to a critical point where gas will begin to desorb from the coal. Production Data analysis of over 100 wells which includes both vertical and deviated in Raniganj East Coalbed Methane (CBM) field, India indicates that wells were not dewatered continuously. This was mainly due to the fact that the wells go on workover and extended periods of pump downtime result in re-saturation of the cleat and fracture system with water, thereby inhibiting gas production. So starting and stopping pumping resets the hydrostatic back pressure and water saturation profiles to initial conditions in the reservoir while the gas content remains unchanged, thereby requiring more pumping to achieve the previous level of gas production. An attempt was made to analyze the problem and through production surveillance of past four years production history, various reasons why continuous dewatering was not achieved were pump failures due to high torque, low torque, low pump efficiency and erratic loading conditions. The causes of these pump failures were gas locking, rod/tubing unscrew, stator damage, hole in tubing, plugged intake screens and insufficient motor cooling, etc. This paper discusses best practices to dewater CBM well after rich experience gained by operator in CBM Raniganj East field from series of trial of artificial lift ESP and PCP pump run in individual wells with design modification by using tailpipes and provides specific recommendations and pump operating parameters to dewater effectively and continuously from both vertical and deviated well.
Konicek, Petr (Institute of Geonics Academy of Sciences) | Soucek, Kamil (Institute of Geonics Academy of Sciences) | Stas, Lubomir (Institute of Geonics Academy of Sciences) | Singh, Rajendra (Central Institute of Mining & Fuel Research (CIMFR, under CSIR)) | Sinha, Amalendu (Central Institute of Mining & Fuel Research (CIMFR, under CSIR))
Abstract: This paper presents geo-mining conditions along with the problems of coal bumps encountered at Chinakuri Mine of ECL (Raniganj coalfield) and Lazy Mine of OKC. Further, the developed and practiced measures at Lazy Mine of OKC to control the coal bump are detailed and analysed to assess their suitability for underground extraction of Dishergarh coal seam of Chinakuri Mine, ECL. It is observed that the conventional techniques, being practiced to release the stress concentrations and to create a network of fissures in the solid accompanying rocks in Indian coalfield, need a complete change. On the basis of this analysis, a suitable method of mining with overlying strata management approach is advised to suit the conditions of the Chinakuri Mine of ECL. 1. INTRODUCTION Out of different rock mechanics problems of underground coal mining of deep seated deposits, coal bump/rock burst is identified (CMRI, 1994) as a major hazard during underground coal mining at greater depth. Coal bump/rock burst engage violent and rapid failure of coal/rock in and around an underground excavation. Sudden release of accumulated elastic stain energy from a rock mass in the free face, created due to excavation, is the origin of this phenomenon and is, mainly, related with the geo-mining conditions of the site, characteristics of the coal/rock mass and stress regime of the area. CIMFR undertook an investigation related to this issue (CMRI, 1994) but this investigation remained limited, mainly, to identify different coal seams of the country likely to pose the coal bump/rock burst problems and their causative factors. Some approaches to control the problems of coal bump/rock bursts were also investigated but their field application achieved partial success. However, this study could project characteristics (Table –1) of some the coal seams and found that the Dishergarh coal seam of Chinakuri Mine (Raniganj Coalfield) is one of the most bump/burst susceptible seam in the country. Recently, CIMFR has collaborated with the Institute of Geonics, Ostrava, the Czech Republic for rock mechanics investigations to meet challenges of strata control of deep underground coal mining. During this collaboration, the success of the Czech counterpart in controlling coal bumps/rock bursts during underground visits of Czech mines is experienced. This paper describes the geo-mining conditions of Chinakuri Mine of ECL and the results of investigations taken to characterise the coal/rock mass of the mine. 2. Chinakuri Mine Chinakuri Colliery 1&2 Pits of ECL is situated in the heart of the Raniganj coalfield on the bank of river Damodar near Asansol city of West Bengal. This is the deepest coal mine in the country, where underground mining is taking place at nearly 700 m depth of cover. Before nationalisation, this mine was owned by M/S. Andrew Yule & Co. and has experienced mining of a number of coal seams by different techniques. However, mining of the Dishergarh coal seam at this mine by bord and pillar and longwall methods of this colliery has always been a problem, mainly due to occurrence of coal bumps.
Chatterjee, R. (Indian School of Mines University) | Gupta, S.K. (Central Mine Planning and Design Institute) | Pal, P.K. (Central Mine Planning and Design Institute) | Srivastava, V.K. (Indian School of Mines University)
Introduction Summary Characterization of coal in term of its physical properties like porosity and permeability has generally been performed on limited sample volumes such as plugs or cores. A methodology is proposed for estimation of permeability for a macro-cleat system of coal from well log derived porosity and from known cleat spacing for Rangamati area of Raniganj Coalfield, India. Data of seven numbers of wells were available from the study area. Geological logs of these boreholes recorded occurrence of four major consistent coalseams (A, B, C & D) at different depths, varying between 53 to 200m in the area. Permeability values of four coalseams with thickness varying between 2-5 m encountered in the seven wells have been correlated with vertical (overburden) stress. Permeability value ranges from 0.5 md at depth of 200 m to 18 md at shallower depth of 53 m while vertical stress decreases from 4.566 MPa to 1.254 MPa respectively. Permeability value of coalseam decreases with increase in vertical stress. Regression analysis between permeability & vertical stress of the coalseams show 2nd order polynomial, as the best fit curves. Goodness of fit (R2) for the 2nd order regressions between vertical stress and permeability for individual coalseams varies between 0.86 and 0.99. Raniganj coalfield covering about 1550 sq. km is the eastern most coalfield of Damodar Valley. It is characterized by half-graben basinal structure with its axis trending broadly in east-west direction and plunging towards west (Ghosh, 2002). The southern flank is truncated by a prominent E-W trending boundary fault (Ghosh, 2002). In general coalseams in India is considered to have low permeability. The permeability of coal seams is usually due to fractures, which occur as cleats. The permeability of the coal matrix is negligible by comparison. Coal cleats are of two types: butt cleats and face cleats, which occur at nearly right angles. The face cleats are continuous and provide paths of higher permeability while butt cleats are non-continuous and terminate at face cleats. Experiments on coal core samples in Japan (Li et al., 2004) had shown that the permeability parallel to bedding plane and cleat strike had the 2.5 times higher than the permeability perpendicular to the bedding plane and 3.0 times higher than in the direction parallel to the bedding plane but perpendicular to the strike. The Raniganj coalfield has two extensive coal measures, Barakar coal measures (Lower Permian) with seven coal seams and Raniganj coal measures (Upper Permian ) with ten coal seams. The thicknesses of the ten productive coal seams in Raniganj Formation are varying from 1 to 11m. Coal thicknesses up to 60 ft (18 m) have been measured where several seams coalesce. The seven wells (5 to 11) from Rangamati block (Fig. 1), located in the eastern part of Raniganj coalfield. Physical properties of coal like porosity and permeability have generally been determined from limited sample volumes such as plugs or cores. No data on the physical properties of the coal seams in and around the study area is available. Therefore a methodology has been proposed for estimation of permeability of the coal seams with macro-cleat system from the well log-derived porosity and from known cleat spacing of the coal seams around Rangamati area.
INTRODUCTION In India, about 50 per cent of the total accidents are attributed to roof and side a Is, the proportion of fatalities on account Of roof fall and that due to side fall being almost equal. Statistics reveal that nearly 50 per cent of the total accidents have taken place by fall of roof rocks of up to 30 cm thickness and in majority of eases the area of the fallen roof rock was less than 10 sq.m.(Prasad 1975). It is generally, therefore, the immediate 30–50 cm of roof which needs close attention to ensure safety against roof falls. In this paper characteristic of weak roofs associated with the mining of some coal seams in the Raniganj Coalfield of India are given and the new technique of securing Such roofs are described. COAL MEASURE STRATA The main coalfields of India are found in the Damodar Valley and the areas adjoining and lie roughly east and west along the 24°N parallel. They belong to the Lower Gondwana period, which is subdivided in ascending order in three series: Talchir, Damodar and Panchet (Table 1). The Talch-irs lie unconformably on Archaean rocks of Precambrian age. Most of the coalfields of India have a number of coal seams. For example, Jharia coalfield has more than 25 workable coal seams, the Raniganj coalfield has seven main coal horizons in the Barakar coal measures and nine in the Raniganj coal measures and some 30 coal seams have been traced in Bokaro coalfield. These seams occur in quick succession, the parting at places being very thin; all are generally banded the bands being from a few milli-metres to several centimetres in thickness. (Table in full paper) The thicker seams have as a rule, more bands. Balls or nodules and rounded fragments of coal are not uncommon. Pyritic intrusions are also very common. The roof and floor of the seams are sandstone or shale. Fireclay as a rule is absent; if present, it is overclay. The strata consist mainly of sandstones and shales, there being various types of gradation into one another, e.g. sandy shale, shaly sandstone, etc. The percentage of sandstone in the strata is usually high (especially in the Raniganj coal measures) and may reach 88% in certain localities. Table 2 shows the relative proportions of different rock types in the Raniganj coal measures. Sandstones form massive deposits and are at times difficult to cave but they form good roof. Shale roofs on the other hand are weak and invariably present roof failure risks. SITES OF INVESTIGATIONS The present study was done in three mines, Dhemo Main, Jamuria 7 & 8 pits and Ranipur Colliery, all in Raniganj coal measures. Roof associated with Raghunathbati seam at Dhemo Main, Taltore seam roof at Jamuria 7 & 8 pits and Dishergarh seam roof at Ranipur Colliery were the subjects of study. In the Raghunathbati seam the workings 194.15m deep lay 156.66m over the goaf of Dishergarh seam.