Paul B. Crawford

Performance of Petroleum Reservoirs Containing Vertical Fractures in the Matrix

A study has been made to determine the effects of random vertical fractures existing in a reservoir matrix on the effective matrix properties and producing characteristics of a well. The study indicated that short vertical fractures may distort the isopotentials by 1% in the vicinity of the fracture. A correlation was developed which showed the effect of fracture density on the producing capacity of a well. The correlation indicated that fracture shape had little effect on producing capacity, but that total fracture length was closely correlated with the producing capacity. Effective values of reservoir permeability were found to correlate closely with fracture density when measured parallel to the direction of flow. (13 refs.)

Effect of Isolated Vertical Fractures Existing in the Reservoir On Fluid Displacement Response

A report is given of a potentiometric model study which was made of the effect of vertical fractures existing in the matrix of the reservoir on the flooding or cycling performance. Fractures can have unusual flow characteristics. Fluid entering one side of a fracture can emerge on either the same or opposite side of the fracture, depending on the particular streamline. Fracture orientation has a great influence on the sweep efficiency. However, sustained fluid injection may still permit large areas to be swept.

PREDICTED AREAL SWEEP EFFICIENCY WHEN USING HORIZONTAL WELLS IN FIVE-SPOT PATTERNS

Abstract Studies have been made to estimate the results when using horizontal wells in five-spot patterns for enhanced oil recovery programmes. It was found that when a horizontal well was used as the centre well of a five-spot pattern, there was very little effect on the areal sweep efficiency for certain well lengths and orientations. A horizontal well does permit increased well injectivity and this could be beneficial when injecting steam into heavy oil reservoirs.

Performance of a Simulated Fractured Matrix Reservoir Subject to a Bottom-Water Drive

The waterflooding performance in homogeneous or isolated layered systems has been well documented in the technical literature; however, the literature does not indicate that work has been conducted on the flooding performance of a fractured matrix reservoir subject to a bottom-water drive. It is generally believed that flooding of a fractured matrix reservoir would not recover much of the oil because the water would move faster through the fracture and there would be an early breakthrough of the water, yet this has not been demonstrated for a bottom-water drive. A model to represent one element of a fractured matrix reservoir was constructed. The model was positioned vertically and water was injected at a constant rate in the bottom and oil was produced from the top of the model. The experiments were made with different initial water saturations using unconsolidated sands. In this study, it was observed that imbibition rather than the direct displacement of oil by water was the dominant mechanism in the recovery of oil from a fractured matrix. It is concluded that thick, fractured matrix reservoirs may be engineered for successful flooding by bottom-water drives.

A comparison of numerical methods for solving large sets of simultaneous equations

Many engineering problems require the numerical solution of several hundred to a few thousand simultaneous equations of the Laplace, Poisson, or Fourier types. These equations occur in the solution of many sci entific problems on heat flow, fluid flow, diffusion, and structural problems, etc. There are many methods available for solving these problems; however, there has been little said about core allocations, execu tion times, and programming difficulty of each method. This paper compares five of the best known methods in terms of core allocation, execution times, and program ming difficulty.

Simulating large flow networks in underground media

This paper presents a new model for simulating the flow behavior describing the efficiency of oil recovery in underground geologic formations. Simulation of the oil displacement problems involve the solution of large numbers of simultaneous equations incorporating the properties of both the fluid and the rock as well as the well patterns. This paper describes in detail the equations used for simulation and the development of the new simulation technique. The application of the new method incorporates a statistical representation of the rock containing the oil and application of flow equations to ascertain the oil recovery efficiency. The oil recovery efficiency is measured by the areal sweep obtained from each separate well pattern by computerized particle tracking of the fluid. The goal is to simulate various oil recovery methods for comparison. This provides a means for selecting a most optimum technique which results in maximum oil recovery and minimum cost. A number of figures are provided to show the results of the simulation technique. Tables and figures show comparisons of the oil recovery efficiency using the new simulation method.

An Improved Reservoir Conduction Heating Model

Steam injection into petroleum reservoirs has become a common method of increasing producing rates and ultimate recovery. In addition, hot fluids are being studied for producing shale oil utilizing conduction heating. This is a study of the temperature distributions resulting from heat conduction. In the new model, superposition distributions resulting from heat conduction. In the new model, superposition of heating rates was used to evaluate temperature distributions for varying heat rates. Assuming that production can be simulated using negative conduction rates, temperature distributions through multiple injection-soak-production cycles were studied. Using this model, it was found that after steam injection, the temperature distribution is characterized by nearly horizontal isotherms. During soaking, little radial spread of the isotherms occurs, but more vertical penetration occurs. Production of fluids results in a removal of heat from above and below the initial heat source. During any production period, a maximum of approx. 36% of the injected heat can be removed in practical times. As a result, heat buildup occurs during successive cycles and both radial and vertical spread of the heated zone occurs. (11 refs.)

Pressure Maintenance Needed Here

Detailed studies have been made of the merits of gas injection into reservoirs of different volatility. Pressure maintenance may consist of the reinjection of all or some fraction of the gas produced, and this may be initiated at any stage in the depletion of the reservoirs. Reservoir oils with high formation volume factors are responsive to gas injection and the recoveries may be increased very substantially depending upon the particular composition of the oil and rock properties. The initiation of full-scale return at some intermediate stage in the depletion may show greater recoveries than partial pressure maintenance initiated at higher pressure. Several studies are presented.

Bi-Radial Model for the Study of Displacement Processes in Pattern-Developed Reservoirs

The behavior of displacement mechanisms through pattern-developed reservoirs has been studied extensively utilizing a great variety of methods. Basically, the methods of study have involved observation of physical laboratory models, analytical solutions, and numerical solutions. All 3 methods have their own unique disadvantages. A stream-line approach has been applied to analytical methods to provide a greater degree of accuracy in the study of displacement processes. This approach has been an improvement over past methods; however, it is still not conducive for studying heterogeneities in the reservoir, and no provision is made for either horizontal or vertical cross-flow components during the displacement program. This paper proposes the study and application whereby the streamlines closely approach the numerical grid of the digital computer. The 5-spot pattern has been treated by aligning a numerical simulator into a bi-radial divergent-convergent grid arrangement.

Numerical simulation of subsurface environment

Subsurface environments are heterogeneous. The permeability and porosity varies from point to point and permeability is only approximately related to porosity. To construct a numerical model that is useful in the analysis of the flow of oil, gas or water in the stratum one must simulate the porous media.