Permian Basin unconventional field developments have several critical subsurface design attributes in focus including well spacing, development sequencing, and hydraulic fracture design. The focus of this study is to accelerate optimization of key hydraulic fracture design parameters and resolve uncertainty in three areas: cluster efficiency, fracture geometry and growth rate, and fracture drainage volume. Reduced uncertainties in these areas leads directly to optimization of key fracture design parameters of perforation design, proppant volume, fluid volume and also the field development decisions like vertical and horizontal well spacing, well sequencing and other FDI mitigations.
A multi-disciplinary team developed a plan to test extended boundaries of fracturing design variable ranges using complementary surveillance methods to achieve the desired uncertainty resolution. Fracturing design decisions were grouped in five designs that covered a range of slurry volume per cluster (SVC) and total proppant to fluid ratio (PFR). A baseline design was executed along with these variations: 40% reduced proppant volume only, 40% increased proppant volume only, 40% reduced fluid volume, and 40% increased fluid volume. To maximize observations, execution varied the designs on a stage-by-stage basis across a batch development. Surveillance technologies applied were ultrasonic image logging, disposable fiber optics, and liquid and oil soluble tracers.
The data collected provided insights to hydraulic fracture design and other field development design attributes. Confirmation was gained that perforation design in use is creating effective cluster efficiency with no impact from the design variation. Analysis of tracers and fiber strain showed that all design variations created fracture geometries far larger than expected. Consistent volume to first response (VFR) measured from fiber strain was also noted in all designs and enabled creation of conceptual fracture height, fracture half length, and fracture growth rate. Tracer interpretations provided many nuanced observations but showed that the stimulated region across the development is highly connected, propped, and draining with low correlation to design variables tested.
The resolution of uncertainty for hydraulic fracture characterization and drainage is directly contributing to business decisions in development. The analysis of cluster efficiency supports continued execution of the preferred perforation design and supports other decisions derived from the fiber strain analysis and tracer analysis. Analysis of fracture geometry and growth rate supports a lower SVC design or wider well spacing that may mitigate excessive well interference and optimize production on a development area basis. Reduced SVC and wider well spacing can be applied in both the vertical and horizontal dimensions. The analysis of fracture drainage volume also supports maintaining a total proppant to fluid ratio at 1:1 and low performance risk down to 0.6:1.
