TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper discusses the performance and productivity of fractured horizontal wells in heterogeneous, tight-gas formations. Production characteristics and flow regimes of unfractured and fractured horizontal wells are documented. The results show that if hydraulic fracturing affects stress distribution to create or rejuvenate natural fractures around the well, productivity of the system is significantly increased. Unless there is significant contrast between the conductivities of the hydraulic and natural fractures, hydraulic fractures may not significantly contribute to the productivity. For extremely tight formations, effective drainage area may be limited to the naturally fractured region around the well and the hydraulic fractures. It is also shown that very long transient flow periods govern the productivity and economics of fractured horizontal wells in tight formations. The results of this study are also applicable to oil production from fractured shale. case D J J J J J = =( 1 4 )

Summary This paper discusses the performance and productivity of fractured horizontal wells in heterogeneous, tight-gas formations. Production characteristics and flow regimes of unfractured and fractured horizontal wells are documented. The results show that if hydraulic fracturing affects stress distribution to create or rejuvenate natural fractures around the well, the productivity of the system is significantly increased. Unless there is significant contrast between the conductivities of the hydraulic and natural fractures, hydraulic fractures may not significantly contribute to the productivity. For extremely tight formations, the effective drainage area may be limited to the naturally fractured region around the well and the hydraulic fractures. It is also shown that very long transient flow periods govern the productivity and economics of fractured horizontal wells in tight formations. The results of this study are also applicable to oil production from fractured shale. Introduction Economic gas and oil production from low permeability reservoirs has been a challenge for the oil and gas industry. Because most of the high permeability reservoirs have been exploited and many low permeability reservoirs remain undeveloped, the latter have taken the industry attention recently. Particular attention has been given to tight-gas reservoirs with permeability in the range of micro-Darcies or below and to oil accumulation in fractured shale. Hydraulically fractured horizontal wells are the proven technology to produce oil and gas from tight formations. Hydraulic fractures reduce well drawndown, increase the productivity of horizontal wells by increasing the surface area in contact with formation, and provide high conductivity paths to the wellbore. Depending on in-situ stress orientation, hydraulic fractures can be parallel (longitudinal) or perpendicular (transverse) to horizontal well axis. Project economics in tight formations, however, depends strongly on well spacing and the number of hydraulic fractures required to drain the reservoir efficiently. Field evidence indicates that the drainage areas of fractured horizontal wells in tight formations may be limited to a rectangular region confining the horizontal well and the transverse hydraulic fractures. Also, there has been evidence that hydraulic fracturing in tight formations changes stresses in fracture drainage area, which could create or rejuvenate natural fractures in the near-vicinity of the horizontal well. This fracture network, which may be characterized as a dual-porosity system, may contribute significantly to improve productivity of the fractured horizontal well. Much work has been done (Soliman et al. 1990; Larsen and Hegre 1994; Temeng and Horne 1995; Raghavan et al. 1997; Wan and Aziz 1999; Al-Kobaisi et al. 2006) to investigate pressure-transient analysis and short- and long-term productivity of horizontal wells with single or multiple hydraulic fractures. The effect of a dual-porosity zone surrounding hydraulic fractures, however, has not been considered in the previous studies. The main objective of this study is to investigate the combined effects of a dual-porosity region and hydraulic fractures on the productivity of horizontal wells. The results presented in this work are based on a semianalytical model developed by Medeiros et al. (2006). The model was derived from the Green's function formulation of the solution for the diffusivity equation (Gringarten and Ramey, 1974, Ozkan and Raghavan, 1991a, 1991b) and has the capability to incorporate local heterogeneities. In this work, we use the semianalytical model to incorporate induced finite-conductivity fractures (transverse and longitudinal) along the horizontal well and naturally fractured zones around the hydraulically fractured horizontal well by using the dual-porosity idealization. We use the example data sets given in Tables 1 through 3 to consider different cases of horizontal wells with and without induced and natural fractures.

This paper discusses the analysis of production data from hydraulically fractured horizontal wells in shale reservoirs. The stimulated volume around the well is simulated by a naturally fractured region. A semianalytical model incorporating the key features of reservoir heterogeneity and the details of hydraulic fracture and wellbore flow is used to present production-decline characteristics in terms of transient-productivity index. Production-decline analysis of fractured horizontal wells in shale-oil and shale-gas formations by transient-productivity index is explained and demonstrated by field applications.

Landslides have frequently occurred in last years, due to the disorderly growth of the cities and the occupation of risk areas by the poor population, causing social, environmental and economic impacts. Urban areas in expansion move to geologically unstable areas and topographically inclined, such as the River Bengalas Basin, located in the city of Nova Friburgo, mountainous region of the State of Rio de Janeiro, Brazil. This article aims to present the model developed and used to evaluate the susceptibility and vulnerability of the River Bengalas Basin to landslides, which in January 2011, with the occurrence of heavy rains, caused landslides that impacted in the death of 429 people in city of Nova Friburgo. For the case study, several investigations have been made related to the areas of the basin, such as slope, soil conditions, lithology, land use and cover, vertical curvature, horizontal curvature, and precipitation data. With this study it was possible to understand how the natural and anthropics elements of the basin are related to the local dynamics of the disasters regarding to their interferences in the induction of landslides; evaluate the effectiveness of the guidelines of the Plano Diretor Participativo do Município de Nova Friburgo regarding the landslides; identify the susceptible and vulnerable basin areas to landslides and calculate the rates of susceptibility and vulnerability to landslides from new calculation model proposed..

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper presents a semianalytical model for the pressuretransient analysis of horizontal wells in composite, layered, and compartmentalized reservoirs. The model divides the reservoir into blocks that represent locally homogeneous substructures of the reservoir and couples the analytical, pressure-transient solutions at the block boundaries. This approach is consistent with the averaging effect of pressure transients and provides an alternative to full numerical modeling of horizontal-well pressure-transient responses in heterogeneous formations. The model can also be generalized for multiple wells of different geometry including multiple laterals.

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Summary Pressure-transient responses of wells in a heterogeneous reservoir are usually computed with numerical models by using fine gridding and very short timesteps. An exceptions to this practice has been the use of analytical, semianalytical, and boundary-element methods for relatively simpler forms of heterogeneity, such as layering or the existence of natural fractures. This paper presents a semianalytical approach to compute pressure transients for more-complex forms of heterogeneity including composite, layered, and compartmentalized reservoirs. In this approach, the reservoir is divided into blocks corresponding to locally homogeneous substructures, and analytical pressure-transient solutions for adjacent blocks are coupled at the boundaries. This approach is consistent with the averaging effect of pressure transients and provides an alternative to full numerical modeling of pressure-transient responses in heterogeneous formations. The validation of the approach is demonstrated in comparison to the analytical solution for horizontal wells in a homogeneous reservoir. Application examples highlight the physical consistency of the approach and demonstrate its capability to model different types of reservoir heterogeneity.

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