Since horizontal drilling practices have become well established, operatorsare focusing on improving completion techniques as well as formation evaluationmethods. Interference pressure testing is on method of formation evaluationthat is a major step in understanding the fluid flow behavior of horizontalwells. The measurement of transient pressure data during interference testingof horizontal wells presents specific design considerations that do not arisein the vertical wells. Multiple interference tests provide valuable informationabout reservoir characteristics such as areal average transmissibility storage, and degree of communication between wells. The key to achieving a successfulinterference test is to take care of the horizontal wellbore from thebeginning. This includes the design and selection of downhole tools as well asthe development of planning and operational stages on a well-by-well basis.This is because no two horizontal wells are alike. This paper presents designcriteria and selection of downhole tools and planning and operational steps forconducting interference tests along the horizontal portion of the well. Thepaper also discusses some of the factors that must be considered beforeembarking on the job. Factors that must be considered include well geometry(lateral length), flow regimes, test durations, type of completion, andwellbore hardware. An example of a simulated interference test designcalculations in a horizontal well is given. The judicious design andutilization of downhole equipment will result in a successful and meaningfulinterference pressure data.
As horizontal well technology continues to gain ground, the next major areaof concern becomes that of obtaining meaningful transient pressure test data.One type of data is interference pressure tests. The term "Interference test"is used to describe the test whereby a detectable pressure drop is measured ata point (in the same or adjacent well) because of production or injection atanother point. That is the test involves more than one point or well in thesimilar reservoir. Generally an active well is produced while the bottom holepressure at a shut-in observation well is measured for several hours or daysdepending onto the anticipated reservoir properties and well spacing. Themeasured pressure history is then analyzed to estimate the inner well formationpermeability and porosity. In the case of horizontal well the interference testwill involve the production of one section of the horizontal part of the wellwhile the bottom-hole shut-in pressure is measured on another part of the holethat is not contributing to flow.