There has been considerable advancement in minifrac analytical techniques since the technology was first introduced.l During the last few years, new techniques have concentrated on the calculation of formation properties blurring the boundaries between the conventional fracture diagnostic analysis techniques and conventional well testing as most of the techniques developed thus far have concentrated on the analysis of the 'before-closure' data?-14 Recently, however, analysis
techniques for after-closure data have been introduced. .
The goal of an after-closure test is to determine various fracture treatment parameters such as fracture-closure pressure, instantaneous shut-in pressure (ISIP), fracture opening pressure, formation leakoff coefficient during a fracturing treatment, and fracture-entry pressure that can influence a fracturing treatment in order to optimize the planned fracture treatment. More modem approaches also focus on obtaining formation permeability and original reservoir pressure.
The goal of this paper is to present a new technique that is deeply based on welltest analysis technology. The well-testing techniques were adapted to the minifrac specialized application. The theoretical techniques have been verified by using a 3-D multi-phase numerical simulator, and then, by analyzing field data.
The pump-in/shut-in test analysis was extended to the calculation of formation permeability by Mayerhofer, et al.9 Instead of the leakoff coefficient used in the conventional model, Mayerhofer, et al assumed that the leakoff is controlled by fracture-face resistance and formation permeability. Using this approach allows the fracture- face resistance and formation permeability to be calculated. This method of analysis is an iterative
technique that depends on having an initial estimate of formation permeability and fracture-face resistance from a specialized plot.
Noting that the technique developed by Mayerhofer et al is "sensitive to deviations from its assumptions," Valko and EconomideslO developed a modified technique that used fixed-fracture geometry to perform the analysis. An important part of their developmental
concept is the deviation from the linear leakoff model; i.e., in their model, the fracture is divided into equal interval segments. The leakoff from various segments may be linear or radial in nature, depending on the location of the segment. The leakoff of fluid into the formation was calculated using classical reservoir techniques that are very similar to the semi-analytical technique developed by Cinco, et al.16
Linking the modified analytical technique developed by Valko and Economides to the G-function analysis and to log-derived parameters, Craig, et all3,14 presented
several successful examples. Although this extension of the analysis has been applied successfully to lower permeability formations; its application to high permeability formations has not been proven.
In application to weak rock, the combination of factors such as composite reservoir and tip screen-out.