Horizontal Well Testing of Isolated Segments
- Thomas P. Frick (Mining University Leoben) | Clemens W. Brand (Mining University Leoben) | Bernhard Schlager (Mining University Leoben) | Michael J. Economides (Texas A&M University)
- Document ID
- Society of Petroleum Engineers
- SPE Journal
- Publication Date
- September 1996
- Document Type
- Journal Paper
- 261 - 274
- 1996. Society of Petroleum Engineers
- 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 5.6.4 Drillstem/Well Testing, 5.6.9 Production Forecasting, 5.1.1 Exploration, Development, Structural Geology, 5.6.3 Pressure Transient Testing, 1.6 Drilling Operations, 2 Well Completion, 2.2.2 Perforating
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A horizontal well test in a large reservoir and with small wellbore storage should produce certain distinct flow regimes. These should lead to the estimation of three permeabilities (along, normal and vertical to the well trajectory) the total well skin effect and, perhaps, the effective (open) well length. The objective of this work is to optimize well test design to obtain the desired flow regimes. It is shown that the important early-time flow regimes can be masked by wellbore storage effects. Therefore, afterflow should be minimized by using downhole shut-in. The storage effects can be estimated with empirical equations. These relationships also mark the beginning of the first interpretable flow regime. It is shown that for very thin formations or in situations where the well is drilled close to the top or bottom boundaries the early radial flow regime may not be seen at all. The length of an almost fully laterally penetrating horizontal well may also distort the late-time radial flow. In both of these instances, calculation of the controlling permeabilities becomes difficult to impossible. It may thus be desirable to test smaller segments of the well. Placing an observation gauge in an isolated segment during the flow testing of another segment can provide further information. It is shown that the derivative of the pressure response in the observation gauge exhibits a characteristic hump. When the hump appears, the permeability along the well axis can be calculated. Testing of isolated segments would also deliver a detailed picture of the skin distribution along an extended horizontal well. From such a test valuable information for enhanced stimulation and selective well completion design can be drawn.
The pressure transient analysis of horizontal wells suffers from two problems:
- A large number of variables influence the pressure response including the effective well length, the vertical standoff (distance from top or bottom boundary) and, more importantly, three permeabilities (rather than a single horizontal as it is for vertical wells.)
- The horizontal well in real field conditions may traverse heterogeneous pressure depletion zones with flow in and out of the well. Damage along the well may be unevenly distributed.
To facilitate horizontal well test design and interpretation it is very helpful if a vertical pilot hole testing sequence is done first. In fact, such testing sequence is essential to prove the desirability of a horizontal well. Once this is demonstrated, the proper well direction must be determined.
The testing sequence in the vertical well consists first of a test under partial penetration. Partial penetration can be accomplished either by drilling only partially into the formation or, more likely, by drilling throughout the net pay and then packing off only a small part (eg. 10 to 20%.).
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