Drilling operations without issues and non-productive time are highly desired by operators. Circulation loss is one of the common issues faced during drilling when a formation is fractured by mud weight or by Equivalent Circulating Density (ECD) exceeding the formation fracture gradient. This makes it necessary to obtain information about in-situ stress and rock strength. Formation Pressure Integrity Tests (FPITs) determine directly the fracture pressure of the formation or test the formation for a safe drilling mud weight window and kick tolerance. Although FPIT is a routine test conducted before drilling each hole section, previous studies and field experience have demonstrated several problems and a lack of unique operational procedures for these tests.
This study examines some of the main issues faced during operation and interpretation of FPITs and possible solutions to eliminate them. We generated a unique database of FPITs which includes all necessary technical and non-technical details about each test and analyzed the discrepancy between surface and downhole pressure data generated while conducting FPITs. We also analyzed pressure build-up behavior versus pumped fluid volume and its similarities with Casing Integrity Tests (CIT). Furthermore, we investigated pressure loss rates after shut-in, and the application of hydraulic impedance testing to improve test quality.
Our analysis of the discrepancy trends indicated that Reservoir Drilling Fluid (RDF) causes more pressure transmission losses than Oil-Based Mud (OBM). We examined more than 50 tests based on pressure build-up behavior versus pumped fluid volume and obtained an empirical equation that only requires the measured depth to give an estimation for the pressure build-up rate. In addition, comparing CIT with FPIT based on pressure build-up rate shows similarities between the tests, and CIT build-up rate values can potentially be used as an initial assumption for FPIT build-up rate. Our findings reveal that pressure loss rate after pump-off is less than 6 psi/min in more than 65% of the Formation Integrity Tests (FITs). We also suggest to use Hydraulic Impedance Testing (HIT) method together with formation strength tests to give a qualitative indication of fracture initiation and a quantitative estimation of fracture dimensions.
|Date of Award||Jul 2021|
|Original language||English (US)|
- Physical Sciences and Engineering
|Supervisor||Tadeusz Patzek (Supervisor)|