Energética ISSN: 0120-9833 [email protected] Universidad Nacional de Colombia Colombia Correa Gutiérrez, Tomás Felipe; Osorio, Nelson; Restrepo Restrepo, Dora Patricia UNCONVENTIONAL NATURAL GAS RESERVOIRS Energética, núm. 41, diciembre-julio, 2009, pp. 61-72 Universidad Nacional de Colombia Medellín, Colombia Available in: http://www.redalyc.org/articulo.oa?id=147012859006 How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative energética UNCONVENTIONAL NATURAL GAS RESERVOIRS YACIMIENTOS NO CONVENCIONALES DE GAS NATURAL Tomás Felipe Correa Gutiérrez1 , Nelson Osorio 2, & Dora Patricia Restrepo Restrepo 3. 1. Mg, Professor Instituto Tecnológico Metropolitano ­ Medellín , Colombia 2. M Sc., engineer in SPT Group Inc. ­ Houston, Texas, EE UU 3. Ph.D., ProfessorUniversidad Nacional de Colombia ­ Medellín, Colombia tomascorrea@ itm.edu.co Recibido para evaluación: 29 de Mayo de 2009 Aceptación: 1 de Junio de 2009 Entrega de versión final: 16 de Junio de 2009 Resumen Este trabajo es una exploración de los diferentes tipos de yacimientos de gas no convencionales en el mundo: mantos de carbón, formaciones apretadas, gas de lutita, gas de hidratos; describiendo aspectos tales como definición, reservas, métodos de producción, problemas ambientales, y económicos asociados a estos. También se mencionan estudios premilitares acerca de estas fuentes energéticas en Colombia. Palabras Clave: Yacimientos no convencionales de gas, Gas lutita, Mantos de carbón, Gas de hidratos, Formaciones apretadas. Abstract This work is an exploration about different unconventional gas reservoirs worldwide: coal bed methane, tight gas, shale gas and gas hydrate; describing aspects such as definition, reserves, production methods, environmental issues and economics. The overview also mentioned preliminary studies about these sources in Colombia. Keywords: Unconventional gas reservoirs, Shale gas, Coal bed methane, Gas hydrate, Tight gas. Energética ­ Número 41, Diciembre de 2008 ­ Julio de 2009, Medellín ­ Colombia ­ ISSN 0120­9833. pp. 61­72 61 Energética ­ Número 41, Diciembre de 2008 ­ Julio de 2009, Medellín ­ Colombia ­ ISSN 0120­9833 1. INTRODUCTION depleted, and the need for energy has increased, the necessity for developing alternate resources has A definition of unconventional gas reservoir is not still become important. According to the U.S. geological precise. An economical definition for unconventional survey(U.S.GS) the unconventional gas resources gas reservoir is, one that cannot be produced at account for a huge prospective reserve worldwide as economic flow rates without assistance from massive shown in Table 1, thus unconventional gas reserves stimulations, treatments or special recovery processes. are becoming the new alternative to supply the global Other technical definition given by geologists and demand for an accessible, available and acceptable engineers refers to unconventional gas like, that one energy resource. which is deposited in a continuous accumulation, such Unconventional natural gas resources have not as shale or coal bed rock itself, rather than being received close attention from natural gas operators, gathered in a trap formed by faults (Mohaghegh, 2005). this is due, in part, because geologic and engineering These accumulations in the basin are caused by the information on unconventional resources is scarce, and very low permeability of the reservoir rock where they natural gas policies and market conditions have been are trapped. Unconventional gas doesn't refer to big unfavorable for development in many countries. In chemical difference from the gas coming out of a addition, there is a chronic shortage of expertise in the conventional well, but instead is more of an allusion to specific technologies needed to successfully develop the unconventional attributes of the reservoir itself and these resources. As a result, only U.S. and Canada how that hydrocarbons are stored there. The name is have had notable developments; however, during the actually most accurately used to describe the last decade development of unconventional natural gas unconventional drilling and production methods that are reservoirs has occurred in Australia, Mexico, needed to get the gas to the wellhead. The common Venezuela, Argentina, Indonesia, China, Russia, Egypt theme is that these lower quality deposits, as far as and Saudi Arabia (NPC, 2007). The main technologies permeability go, require improved technology and developing to be feasible economical production of adequate gas prices before they can be developed and unconventional are been doing in US as mentioned produced economically. The commercial production is before so special emphasis along this paper is going immature and development of tight sand gas, coal bed to be done on US. Futures studies necessarily will be methane, shale gas is undertaken mainly in the U.S done in South America and rest of the world as the and Canada up to date. In the past, technical challenges demand of new resources increase and conventional and cost issues around producing unconventional gas reservoirs are mature. This article gives a brief review deterred resource exploration and development; of unconventional gas reservoirs such as coal bed however, as conventional gas resources are becoming methane, gas hydrate, shale gas and tight gas Table 1. Unconventional Gas Reservoir Reserves Worldwide in Tcf ([Steven, 2004) Region CBM Shale Gas Tight gas Total North America 3017 3840 1371 8228 Latin America 39 2116 1293 3448 Europe 275 548 431 1254 Formet soviet Union 3917 627 901 5485 ME and N, Africa 0 2547 823 3370 Sub Saharan Africa 39 274 784 1097 Centrally. Planned Asia and China 1215 3256 353 5094 Pacific 470 2312 705 3487 other Asia Pacific 0 313 549 862 South Asia 39 0 196 235 World 9061 16103 7406 32506 2. COAL BED METHANE (CBM) topography, water saturation and water chemistry. During the earliest stage of coal formation, the sub­ Coalbed Methane is natural gas produced from coal bituminous phase, biogenic methane is generated by seams where coal is both the source rock and reservoir. bacterial action under defined conditions of low Each CBM basin is unique in terms of geology, temperature (1220F), low depth and low pressure; 62 Unconventional natural gas reservoirs ­ Correa, Osorio & Restrepo. methane is stored within the coal in internal surfaces Gas storage capacity or gas content of coal reservoirs is with subsequent release of water. Further burial and reported in units of scf/ton and is determined by measuring increased temperature (above 122 0 F) generates the volume of gas released from a coal sample while thermogenic methane; in this phase coal reaches a rank varying the pressure at isothermal conditions. of bituminous characterized by an increase of volatile matter and hydrocarbons in place. After excessive 2.1. Reserves burial and about 300 0F the maximum generation of methane takes place, then the gas content of coal As it is shown in Table No 1 coal bed methane reserves increases with depth, pressure and coal rank (Warlick, are spread out worldwide and mainly located in Russia, 2006). High pressures below the surface retain some North America and Asia. It represents around 10% of methane in the coal matrix in an adsorbed state; this the total unconventional gas resources worldwide. In high pressure is created by both overburden and by Colombia Coalbed methane assessments show the water that is contained in the coal matrix. Coalbed potential reserves in a range between 3 to 17 Tcf methane is made up of basically 90% or more methane (Conpes, 2008). Major potential basins are mainly as the name suggests; other gases that may exist in located in Bogota plateau, Guaduas formation, coalbed deposits in trace amounts are ethane, propane, Guachinte­Ferreira formation, Cauca basin, Catatumbo butane, carbon dioxide and nitrogen. The heating value basin, Llanos basin, Middle Magdalena basin and of this gas is usually less than 1000 Btu/scf, because Cauca river basin (Conpes, 2008. Luna, 2004). Proof the CO content has no heating value. of potential for CBM is that along these carboniferous 2 regions bituminous coal with up to 35% in volatile matter The geologic characteristics of the coalbed methane is present (UPME, 2005). Colombia has resources of reservoirs are complex because they correspond to coal; even tough, they have not been studied on deep naturally fractured layers with two systems of porosities Drummond company which produce carbon from (Collet, 2001) as shown in Figure 1. A primary porosity Colombia has estimated 4.7 Tcf of proved reserves system is created by microporous with extremely low and 17 Tcf of potential Reserves (Drummond, 2009). permeability making it impermeable to the adsorbed Table 2 shows Colombian regions and potential and gas and non accessible to water, so desorbed gas only proved reserves in each state. can flow through the system by diffusion. A secondary porosity system is defined by a set of natural fractures, Table 2. CBM in Colombian regions (Zamora, 2009) cracks and fissures, well known as cleats or macroporous; they are the responsible of the Colombian Coal Bed Methane permeability in the coal. Region Carbon to Carbon, GIP Proved produce TIP, TIP Tcf reserves(Tcf) 10 9 ton. M 10 9 ton.m Guajira 4.8 2.4 Cesar 4.5 13.6 6.9 3.4 Córdoba 6.6 19.7 8.8 ­ Antioquia 0.7 2.2 0.5 ­ Valle del Cauca 0.5 1.4 0.3 ­ Huila 0.2 0.7 0.0 ­ Cundinamarca 0.0 0.0 1.6 0.8 Boyacá 1.5 4.4 1.8 0.9 Santander 1.7 5.2 0.5 ­ N.Santander 0.5 1.4 0.8 ­ Total 0.8 2.4 17.8 7.5 17 51 2.2. Production In order to release the methane, producers drill holes to reach the coal layers, and large quantities of water must be pumped out to lower the pressure and help desorption of the gas from the rock, a typical curve of Figure 1.