Experimental Study of Formation Damage during Underbalanced-Drilling in Naturally Fractured Formations

Abstract

This paper describes an experimental investigation of formation damage in a fractured carbonate core sample under underbalanced drilling (UBD) conditions. A major portion of this study has concentrated on problems which are often associated with UBD and the development of a detailed protocol for proper design and execution of an UBD program. Formation damage effects, which may occur even if the underbalanced pressure condition is maintained 100% of the time during drilling operation, have been studied. One major concern for formation damage during UBD operations is the loss of the underbalanced pressure condition. Hence, it becomes vital to evaluate the sensitivity of the formation to the effect of an overbalanced pulse situation. The paper investigates the effect of short pulse overbalance pressure during underbalanced conditions in a fractured chalk core sample. Special core tests using a specially designed core holder are conducted on the subject reservoir core. Both overbalance and underbalanced tests were conducted with four UBD drilling fluids. Core testing includes measurements of the initial permeability and return permeability under two different pressure conditions (underbalanced and overbalanced). Then the procedure is followed by applying a differential pressure on the core samples to mimic the drawdown effect to determine the return permeability capacity. In both UBD and short pulse OBP four mud formulations are used which are: lab oil, brine (3% KCL), water-based mud (bentonite with XC polymer) and fresh water. The return permeability measurements show that a lab oil system performed fairly well during UBD and short OB conditions. The results indicate that a short overbalance pressure provides a OPEN ACCESSEnergies 2011, 4 1729 significant reduction in permeability of the fractured formations. In most tests, even application of a high drawdown pressure during production cannot restore the initial permeability by more than 40%.

Formation Damage due to Drilling and Fracturing Fluids and Its Solution for Tight Naturally Fractured Sandstone Reservoirs

“…Results show a good consistency and all data points fall on a curve where effective permeability ( ) is proportional to the third power of fracture width ( ). This agrees on the classic formula on estimating fracture permeability in the laminar flow regime [45,46].…”

A New Experimental Approach for Hydraulic Fracturing Fluid Damage of Ultradeep Tight Gas Formation

“…A novel unsteady-state formation damage evaluation method based on pressure transmission and pressure decay theories was used to investigate the FFD mechanism. The previous researchers well documented the pressure decay theory and pressure transmission theory as well as the experimental procedures ( [25][26][27][28][29][30][31][32][33][34]). The permeability measurement theory of the pressure decay method can be described in equations (1) and (2).…”

Investigations into the coiled tubing partial underbalanced drilling (CT-PUBD) technique for drilling hard formations

“…(3) According to the test performance, a small flow rate (13 L/s) of drilling fluid can have a high efficiency on the bottom hole cleaning, providing guidance on releasing the cuttings deposit problem. (4) Using a lowdensity drilling fluid near the drill bit can reduce the reservoir damage (Salimi and Ghalambor 2011). Thus, it can effectively protect the productivity of the reservoir and enhance the production capacity of oil and gas wells.…”

“…Compared to the overbalanced drilling method, the UBD technique using low mud weight can minimize lost circulation, differential sticking and formation damage in depleted and fractured reservoirs (Salimi and Ghalambor 2011). Using the UBD technique, the bottom hole pressure can be controlled to be lower than the formation pressure.…”