DFIT Survey for Reservoir Evaluation of a Low Permeability Formation during Well Testing
Authors: Kulyatin Oleg , Lomukhin Alexander , Prokhorov Alexey , Romashkin Sergey , Samoilov Mikhail 
Published: October 2019

Conventional well testing methods and techniques on low permeability formation are not practical and inefficient due to weak natural flow rates. For such formations performing hydraulic fracturing is planned to increase flow rates and engage formation into flowing, but at such status it is impractical to carry out hydrodynamic testing survey, as it required long duration of survey, up to several weeks and months.

As a sound option for low permeability formation could serve Diagnostic Fracture Injection Test (DFIT) survey. The main interest of this paper was to execute DFIT survey, full cycle from planning to wellsite job execution, obtain the required data, results and confidence to decide if DFIT is effective method to practice at exploration and appraisal phase.

For performing reliable evaluation of formation permeability it is important to design and execute fracturing job in optimal to obtaining descriptive and timely formation response. The target fluid filtration "pseudo-radial" regime takes place at latest stage of pressure fall-off, develops at investigation radius beyond fracture length and usually non-observed, as takes tremendous time for low permeability formation.

In frame of present project, the intention was to initiate compact fracture with small length, therefore to be capable to register pseudoradial flow regime at reasonably short time, up-to three days. DFIT survey with small length fracture was executed with well shut-in bottomhole with tester valve.

For first time on low permeability formations in Urengoy area DFIT survey was performed with well shut-in bottomhole with tester valve immediately after fracture placement. High resolution descriptive bottomhole data was gathered. Targeted "pseudo-radial" regime was achieved starting at 50 hours and lasted to the end of 72 hours fall-off period duration. DFIT data processing and After-closure-analysis (ACA) allowed deriving initial pressure and fluid mobility in remote formation zone. DFIT data processing and After-closure-analysis (ACA) was carried out in three alternative software packages, data discrepancies were analyzed for conclusions and decision for future usage.

Within complex well testing program set of formation evaluation parameters – formation pressure, permeability and skin – was targeted to be extracted from various conventional methods, such as initial Drill Stem Test (DST) with short opened and closed periods, extended flowing on fixed chokes with stabilized rates, descriptive build-up at end of flow testing sequence. These evaluated formation parameters are to be compared with those, derived from DFIT survey to justify DFIT survey applicability and uncertainties.

Based on data, results and experience gathered through project execution built our confidence in claiming DFIT as sound instrument for evaluating properties of low permeability formation wells. This applies for wells at exploration and appraisal phase, and potentially can bring corresponding benefits when expanded to exploitation drilling wells to be put into production.