Multi-Layer Vertical DFIT and Mini-Fracture Assessment in an Unconventional Tight Shale Vertical Well

Abstract

The main objective of this study is to present the findings of an assessment conducted on an unconventional vertical well, which aimed to acquire closure pressure estimates at multiple depth points, evaluate fracture height propagation at specific sections, identify fracture barriers, and relevant reservoir properties at different intervened sections. The subjected well passed through seven different sections, some of which were considered potential prolific targets while others were considered fracturing barriers. The first objective of the well was to acquire multiple closure pressure values at multiple depths that can later be used to calibrate stress models. To meet that objective, a diagnostic fracture injection test (DFIT) was conducted at the seven different sections with variable monitoring durations. Downhole memory gauges were installed to minimize uncertainties related to pressure fluctuations in surface gauges which could be attributed to day to night temperature variations. Out of the seven DFITs, closure pressure was estimated in two out of the seven sections. The second objective was to assess vertical fracture height growth in two of the most prolific sections, with a design objective of mimicking a single cluster in a horizontal lateral. To achieve that, a mini fracture at pre-determined pumping rates and volumes was pumped followed by three high resolution temperature (HRT) logs acquired at 2-hour gap intervals, yielding cool down and warm up profiles that reflect height growth. For both mini fractures pumped at the two sections, estimation of maximum fracture height was obtained. Overlapping results from both mini fracture tests indicated that the two sections did not interfere with each other. The novelty of this study lies in its implementation rarity in unconventional fields due to the uncommonness of vertical unconventional wells. The information gathered from this study provides key parameters for understanding fracture behavior in multiple vertical sections, which are essential in the design of stimulation operations and future decision-making processes.