Richard A. Morse

Productivity of Vertically Fractured Wells Prior to Stabilized Flow

%vera! ZN.Ithors’ -’ !IWe nrewm!ix! rmmwx on the e-ff.cK ~----~-r --. . . . . .. ---of hydraulic fracturing on well productivity. Most of this work has been concerned with the effects of fracturing on “stabilized” or “semistead~ state” productivity. Prats eI al.’ investigated analytically the effects of vertical fractures of infinite flow capacity on well productivity as a function of time. Their results shQwed a SignifiC~n[variation in mrn~ll~t;u;~~~ nw~r tk~ y.-.. ”-....., “.W, ...” range of dimensionless times (r~) from 0.01 to 0.5. Productivity for one set of reservoir conditions showed a variation of about eightfold over this range of dimensionless time. Morse and HolditchG indicated fractured well productivities varying by factors in excess of 10 over a real-time range of a few weeks or months under some resemoir conditions. The objective of this work was to make a systematic study of both constant rate and constant pressure well productivities for a range of reservoir rock and fluid properties and for vertical fractures of various lengths.

Oil Production from Fractured Reservoirs by Water Displacement

A study has been made of the flow behavior of fractured oil reservoirs produced by water displacement. A 2-dimensional numerical model capable of simulating flow of water and oil in the matrix blocks as well as in the fractures has been developed. The validity of the model has been checked against data from a laboratory experiment involving a matrix-fracture system. Good agreement was observed between the laboratory and simulation results. By means of numerical simulation, the effects of production rate and fracture flow capacity on the production history and ultimate oil recovery of a fractured system have been evaluated. Results are presented for a single matrix-block system where the block is surrounded by horizontal and vertical fractures. Production rates ranging from 0.05 to 5 times the gravity reference rate of the matrix, and fracture flow capacities ranging from 0.1 to 10 times the flow capacity of the matrix are included in the investigation. (32 refs.)

The Effects Of Various Reservoir And Well Parameters On Water Coning Performance

Most research on water coning has been directed toward minimizing water production by reduced well penetration or production rate control. Hovvzver, complete depletion of an oilcolumn underlain by water will necessarily be accompanies by considerable water production, at least in the latter stages of depletion. By means of numerical simulation a systematic study W4S made of the effects of reservoir and well parameters on water coning performance. Included were the effects of aquifer thickness, well penetration, pressure drawdown, and horizontal to vertical permeability ratio. These studies revealed that higher water-oil ratios, at every stage of depletion, resulted from increasing well penetration or increasing pressure drawdown at the producing well. Accompanying the increase in water-oil ratio is an increase in oilproduction rate of the same magnitude thus de -

Gas Injection for Upstructure Oil Drainage

Oil recovery from high-relief reservoirs can be increased by down-structure gas injection. In this process, often called Attic Oil Recovery, gas is injected in the structurally highest well in the reservoir. The injected gas well migrate up-structure, forming a secondary gas cap and displacing oil downward. Many authors have reported on field applications of the Attic Oil Recovery process. In 1971, Combs and Knezek published theoretical guildelines and field data concerning the maximum gas/oil segregation rate and the minimum and actual gas requirements to recovery one barrel of oil. This work presents results of a numerical model study of an Attic Oil Recovery process and defines the variables that control the reservoir performance of a successful project. A method is presented to calculate the required gas injection volumes. 15 references.

A Numerical Model Study of Gravitational Effects and Production Rate on Solution Gas Drive Performance of Oil Reservoirs

A variety of mathematical models and solution techniques have been developed to calculate fluid flow in 3 dimensions and accounting for all known factors affecting flow in a system flowing 1, 2 or 3 phases. Numerical model simulations have been made of solution gas-drive performances covering a 500-fold range of oil production rates. By scaling theory, confirmed by calculation, these results were extended to all levels of permeability. Two-dimensional simulations were made in which the maximum total horizontal pressure drop was held to less than 20% of the average absolute pressure. These tests showed such small horizontal saturation gradients that comparative one-dimensional tests were made for the same producing rates. The model simulated was a linear segment 1,400 ft long x 25 ft high x 1 ft thick. For the 101-md model, oil-production rates ranges from 0.1 to 50.0 bpd. The production rates simulated correspond to a range of 2.48 to 1,280% of oil in place produced per year. At low rates vertical segregation was noted, and this affected the GOR and pressure performance. (40 refs.)