Underbalanced Drilling (UBD)
We deliberately reverse the pressure relationship between the well and the reservoir, so that the reservoir flows into the well as drilling takes place. This protects productivity, reduces losses, and provides real-time reservoir information, as long as the entire system can maintain underbalanced conditions.
Working Methodology
Our approach combines reservoir evaluation, multi-phase design, and surface system control at every stage of the project
1. Candidate selection
Evaluation of the reservoir type and its susceptibility to formation damage, reservoir pressure, geomechanical and wellbore stability conditions, historical losses and field history, to determine if the reservoir justifies underbalanced drilling.
2. Detailed geomechanical analysis
Modeling the wellbore's stability under reduced support pressure is used to confirm that the candidate can sustain the underbalanced condition. This is the constraint that most frequently disqualifies it.
3. Fluid system selection
Gasified liquid with inert gas or natural gas; foam; mist or gas only; or light liquid without gas injection, under natural underbalanced conditions. The selection depends on the reservoir pressure and well conditions.
4. Multiphase hydraulic design
Modeling of multiphase flow, gas and liquid injection rates, surface backpressure, and wellbore cleaning capacity.
5. Surface system engineering
Rotary control device, choke manifold, four-phase separation, gas injection, and controlled flaring and utilisation of the produced hydrocarbons. All sized by the expected influx, not by the wellbore diameter.
6. Operations and Contingencies Matrix
Operating limits under balance, H₂S and produced fluids management, erosion control, escalation criteria and critical procedures agreed before mobilization.
7. Execution and reservoir monitoring
Drilling with controlled influx and continuous measurement of gas, liquid and pressure to identify producing intervals while drilling.
8. Evaluation and closure
Performance analysis, reservoir characterization obtained during drilling, and technical documentation of the project.
