Fractal and power law distributions have been found in the past to be useful for modeling some reservoir properties following the assumptions of constant shape and self-similarity. This study shows, however, that pore throat apertures, fracture apertures, petrophysical and drill cuttings properties of unconventional formations are better matched with a variable shape distribution model (as opposed to constant shape). This permits better reservoir characterization and forecasting of reservoir performance.
Pore throat apertures, fracture apertures, petrophysical properties and drill cutting sizes from tight and shale reservoirs are shown to follow trends that match the variable shape distribution model (VSD) with coefficients of determination (R2) that are generally larger than 0.99. The good fit of the actual data with the VSD allows more rigorous characterization of these properties for use in mathematical models. Data that could not be described previously by a single equation can now be matched uniquely by the VSD. Examples are presented using data from conventional, tight and shale formations found in Canada, the United States, China, Mexico and Australia.
In addition, the study shows that the size of cuttings drilled in vertical and horizontal wells can also be matched with the VSD. This allows the use of drill cuttings, an important direct source of information, for quantitative evaluation of reservoir and rock mechanics properties. The results can be used for improved design of stimulation jobs including multi stage hydraulic fracturing in horizontal wells. This is important as the amount of information collected in horizontal wells drilled through out tight formations, including cores and well logs, is limited in most cases.
It is concluded that the VSD is a valuable tool that has significant potential for applications in conventional, low and ultra-low permeability formations and for evaluating distribution of rock properties at the micro and nano-scale.
Fractal geometry was introduced by Mandelbrot (1982) in his seminal work "The Fractal Geometry of Nature.?? He indicated that this type of geometry applies to many irregular objects in nature. Since then, fractals have been shown to be useful in many disciplines including geology, petroleum engineering, earthquakes, and economics to name a few. In geology, the approach has been used, for example, to evaluate the distribution of natural fractures in outcrops and reservoir rocks; also for evaluating stratigraphic units. In petroleum engineering, they have been used in efforts to capture the distribution of natural fractures for well test analysis. In the case of telluric movements, fractals have been used to evaluate very small to very large earthquakes. In economics, fractals have been used to analyze the distribution of income amongst populations. In the case of the oil and gas industry as a whole, fractal geometry has been used for estimating the spatial distribution of hydrocarbon accumulations (Barton and Scholz, 1995).
Tsar, Mitchel (Curtin University) | Bahrami, Hassan (Curtin University) | Rezaee, Reza (Curtin University) | Murickan, Geeno (Curtin University) | Mehmood, Sultan (Curtin University) | Ghasemi, Mohsen (Curtin University) | Ameri, Abolfazl | Mehdizadeh, Mahna
Tight gas reservoirs are mainly characterized by low matrix permeability and significant damage. During drilling and fracturing of tight formations, wellbore liquid invades into tight formation and increases water saturation around wellbore and eventually reduces permeability near wellbore or adjacent to fracture wings. The damage to permeability caused by invasion of liquid into tight formation is controlled by capillary pressure and relative permeability curves.
The phase trap damage is one of the main concerns in use of water based drilling or fracturing fluid, since due to high critical water saturation, strong capillary pressure, and sensitivity of tight sand to water. Therefore, use of oil based mud may be preferred in drilling or fracturing of tight formation. However invasion of oil filtrate into tight formation may result in a three-phase relative permeability curves in invaded zone in presence of reservoir gas and initial water, which may differently affect damage and productivity of tight gas reservoirs.
This study evaluates phase trap damage in water-based in comparison with oil-based drilled or fractured tight gas reservoir. Reservoir simulation is used to study the effect of relative permeability curves on phase trap damage and well productivity, based on reservoir and core data from a West Australian tight gas reservoir. The results highlights benefits of using oil-based fluids in drilling and fracturing of tight gas reservoirs in term of improving well productivity.
Streamline and streamtube methods have been used in fluid flow computations for many years. Early applications for hydrocarbon reservoir simulation were first reported by Fay and Pratts in the 1950s. Streamline-based flow simulation has made significant advances in the last 15 years. Today's simulators are fully three-dimensional and fully compressible and they account for gravity as well as complex well controls. Most recent advances also allow for compositional and thermal displacements.
In this paper, we present a comprehensive review of the evolution and advancement of streamline simulation technology. This paper offers a general overview of most of the material available in the literature on the subject. This work includes the review of more than 200 technical papers and gives a chronological advancement of streamline simulation technology from 1996 to 2011. Firstly, three major areas are identified. These are development of streamline simulators, enhancements to current streamline simulators and applications. In view of the fact that this state of-the-art technology has been employed for a wide range of applications, we defined three major application areas that symbolize the relevance and validity of streamline simulation in addressing reservoir engineering concerns. These are history matching, reservoir management and upscaling, ranking and characterization of fine-grid geological models.
Streamline simulation has undergone several phases within its short stretch in the petroleum industry. Initially, the main focus was on the speed advantage and less on fluid flow physics. Next, the focus was shifted to extend its applicability to more complex issues such as compositional and thermal simulations, which require the inclusion of more physics, and potentially reducing the advantage of computational time. Recently, the focus has shifted towards the application of streamline technologies to areas where it can complement finite difference simulation such as revealing important information about drainage areas, flood optimization and improvement of sweep efficiency, quantifying uncertainties, etc.
Introduction of Streamlines Simulation
Streamlines are integrated curves that are locally tangential to a defined velocity field at a given instant in time (Datta-Gupta 2007 and Thiele et al. 2010) as illustrated in Figure 1. Modeling fluid flow and transport using streamlines dates back to the study of well pattern and total recovery by Muskat and Wyckoff in 1934. Streamline-based flow simulation has made significant advances in the last 15 years. A great historical overview of the earlier streamlines work was presented by Batycky (1997), Datta-Gupta and King (1998), Thiele (2001), Moreno et al. (2004), Datta-Gupta (2007).
Ideally, geoscientists would like to have quantitative information about rock properties, along with information about fluid content of potential reservoirs relatively directly from the seismic as this information is available as oppose to the well data. Historically, seismic images have stopped short of delivering this, as the seismic bandwidth was limited due to the conventional streamer design and acquisition method.
The ability to predict reservoir properties away from the well using seismic information is a key element in quantitative interpretation. Quantitative seismic interpretation combines various types of data: well, seismic and seismic interpretation or geological prior information. Thus, this workflow is integrated and the quality and accuracy of each individual constituent is of great importance to the accurately estimate the volume of hydrocarbon in place in a particular reservoir interval.
Seismic plays a key role in this, and if the seismic data contains very strong low frequency information and the seismic image is of high quality/resolution, it is possible to directly estimate the absolute impedance at each point within a seismic volume.
Over the last few years, new acquisition methods and technologies exist aiming to provide a broader seismic bandwidth: streamer towed shallow at the front and going deeper at the mid of the streamer, towed acquisition with some streamers at shallow and deeper depth, and the dual-sensor towed streamer.
These new broadband seismic data volumes are bringing the seismic a step closer to the reservoir and this is what we will try to demonstrate in this presentation. We will have the latest look at some of the newest and most exciting improvements in reliably unraveling the rock properties from the 3D seismic data.
This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 149472, "Analyzing Variable-Rate/-Pressure Data in Transient- Linear Flow in Unconventional Gas Reservoirs," by P. Liang, SPE, L. Mattar, SPE, and S. Moghadam, SPE, Fekete Associates, prepared for the 2011 Canadian Unconventional Resources Conference, Calgary, 15-17 November. The paper has not been peer reviewed.