Interference tests provide valuable information about reservoir characteristics such as areal average transmissivity, storativity, and degree of communication between well. Due to the larger radius of influence and larger contact area of a horizontal well with the formation than its vertical counterpart, the transmissivity and storativity obtained from interference testing of horizontal wells would be much more representative of the formation than the ones obtained from interference resting of vertical wells.

This paper provides the dimensionless pressure drop and dimensionless pressure derivative type curves for interference resting of horizontal wells and the appropriate equations to be used in conjunction with the type curves in order to determine transmissivity and storativity from field data. Solutions were also obtained for interference testing between horizontal and vertical wells. The deviation of this solution from the exponential integral solution is explained. Dimensionless Lime and dimensionless distance criteria is esla1llished for a particular set of dimensionless parameters to explain this deviation, Guidelines are given for interference test design.


During the last 15 years, significant advances in drilling technology have made it possible to drill horizontally. A horizontal well, due to its large flow are, may be several limes more productive than a vertical well draining the same volume.

In B vertical well fractured by massive hydraulic fracturing, it is difficult to obtain an infinite conductivity fracture. In addition, fracture conductivity decreases with time. One reason is because of the problems associated with the proppant transport. The other reasons are due to the proppant embedment and also proppants not being able to with stand in-situ stresses of the rock; thus they break down, causing fracture conductivity to decrease with time. However, B horizontal wellbore offers a permanent infinite conductivity fluid flow path. Also, in reservoirs where the bottom water or gas cap renders fracturing difficult, a horizontal well offers an alternative to obtain high production rates without gas and water coning. The possibility of drilling horizontal wells should be evaluated for.

  • Tight reservoirs, especially if vertical fractures are suspected.

  • Naturally fractured reservoirs containing vertical fractures.

  • Unconventional low permeability gas reservoirs.

  • Thin formation

  • Thicker zones of marginal permeability.

  • Thin oil columns, especially when bottom water and/or gas cap is present

  • Chalk formations which contain natural fractures.

  • Old reservoirs that no longer have adequate drivmechanisms.

  • Producing reservoirs with extremely high dip angles.

  • Secondary recovery operations (increased injection area and improved sweep efficiency).

  • Heavy oil reservoirs.

  • Reduction of turbulence in gas reservoirs.

  • Exploration and development of inaccessible locations.

  • Areas Where environmental concerns minimize number of surface locations.

Western exploration activity in North Dakota has been focused on developing the Bakken shale formation reserves with horizontal drilling. The Bakken shale is estimated to have 10 billion barrels of oil which indicates its enormous economic importance and the role that horizontal drilling can play in exploiting these resources. The objectives behind dn1ling horizontal wells in the Bakken shale are to increase the effective drainage area and maximize recoverable reserves and to increase productivity by encountering more

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