Horizontal Well Pressure Analysis
- E. Ozkan (U. of Tulsa) | R. Raghavan (U. of Tulsa) | S.D. Joshi (Phillips Petroleum Co.)
- Document ID
- Society of Petroleum Engineers
- SPE Formation Evaluation
- Publication Date
- December 1989
- Document Type
- Journal Paper
- 567 - 575
- 1989. Society of Petroleum Engineers
- 5.8.7 Carbonate Reservoir, 5.6.1 Open hole/cased hole log analysis, 4.1.2 Separation and Treating, 1.6.6 Directional Drilling, 5.8.6 Naturally Fractured Reservoir, 4.1.5 Processing Equipment, 1.6 Drilling Operations, 5.6.4 Drillstem/Well Testing
- 11 in the last 30 days
- 2,312 since 2007
- Show more detail
- View rights & permissions
|SPE Member Price:||USD 10.00|
|SPE Non-Member Price:||USD 30.00|
This paper presents an analysis of the pressure transient behavior of a horizontal well or a drainhole. The performance of horizontal wells and fully penetrating vertical fractures is compared. Dimensionless wellbore pressures are computed for two classical boundary conditions; namely infinite-conductivity and uniform-flux. Results are presented as pseudoskin factors and as type curves. In addition to conventional pressure versus time type curves, derivative type curves using pressure-time predictions are presented. The derivative approach we discuss here is new to the petroleum literature and is applicable to a broader range of problems than that considered here.
Computations suggest that horizontal well productivity is governed by two parameters: 1) the dimensionless well length, LD (LD = L / (2h) , where L is the length of the well, h is the formation thickness, and kz and k are the vertical and horizontal permeabilities, respectively), and 2) the dimensionless well radius, rwD, (the ratio of well radius to well half-length if the formation is assumed to be isotropic). Results indicate that horizontal well productivity (infinite-conductivity) is almost identical to that of a fully penetrating vertical fracture of infinite-conductivity if the dimensionless horizontal well length, LD, is greater than 4.0. This result shows that horizontal wells may perform better than vertically fractured wells, if non-ideal aspects associated with vertically fractured wells such as limited conductivity or height, are taken into account.
Results have been obtained for LD in the range 0.1 less than LD less than 100 and dimensionless well radius, rwD, in the range 10(-4) less than rwD less than 10(-2); these ranges should encompass expected values of horizontal well length, reservoir height, and ratio of vertical and horizontal permeability. Pressure responses and pseudoskin factors are calculated for four different well locations within the productive interval. The pseudoskin factors are insensitive to well location.
A review of production performance over the past few years, conclusively establishes the advantages of horizontal wells and drainholes. Drainholes are normally drilled from existing vertical wells and extend 100 feet to 500 feet in either direction. Horizontal wells involve the drilling of new wells and are usually 1000 feet to 2000 feet long. Both completions, like fractured wells, are intended to provide a large surface area for fluid withdrawal and thus improve productivity. These completions have been found to be effective in (i) some naturally fractured reservoirs, (ii) reservoirs wherein gas and/or water coning problems preclude the efficient operation of vertical wells, (iii) thin reservoirs, and (iv) reservoirs with high vertical permeability. Disadvantages of these completions include high drilling costs and the inability to produce contagious zones separated by impermeable layers via a single wellbore.
For purposes of modeling well behavior, horizontal wells and drainholes can be treated similarly. Thus, unless specifically stated, the term horizontal well will include both types of completions.
To be a commercial method of completion, at least for primary recovery, horizontal well productivity must be comparable to the productivity of a vertically fractured well. It is not sufficient to compare horizontal well productivity with unstimulated vertical wells. Similar observations have been made in Refs. 1 and 2. Thus, in this work responses for vertically fractured wells are used as a basis for comparison. (A horizontal well may be viewed as a fracture with limited height, however, this does not imply that horizontal well productivity will never be comparable to that of a vertically fractured well.)
The transient behavior of horizontal wells and the characteristics of response curves have been considered in Refs. 3 - 5.
|File Size||857 KB||Number of Pages||9|