Due to the special working environment, offshore drilling operation faces multiple challenges such as narrow pressure margin, difficulty in detecting down hole conditions and high operational risk. A new managed pressure drilling equipment is developed and named as pressure control drilling system-I (PCDS-I), which integrates the techniques of constant bottomhole pressure and microflux control and it is capable of performing the underbalanced, near-balanced and overbalanced MPD drilling as required. This new-type managed pressure drilling equipment is applied in several offshore wells to perform near-balanced managed pressure drilling operations with great success.
Before utilizations, real-time hydraulic calculations are conducted based on the field data and back pressures are designed for reducing the density of drilling fluid. In the field applications, the PCDS-I precisely keeps the bottomhole pressure constant and minimizes the pressure fluctuations, creating a near-balanced drilling condition. In addition to the real-time bottomhole pressure measured by pressure while drilling (PWD) equipment, the pumping rate and returning rate of drilling fluid are monitored by the PCDS-I. The cumulative pumping and returning volumes of drilling fluid and their difference are calculated by a program and compared with the volumes of drilling tools, providing a new way to detect the overflow and lost circulation in the tripping operations. Data of other operators are monitored and analyzed, such as logging data, providing reference for detecting the downhole condition and determining the back pressure.
Multiple drilling processes are successfully completed without any issue occurs with the assistance of this new managed pressure drilling equipment, including drilling, ma king connections, tripping, snubbing and circulating, etc. Cooperated with the PCDS-I, the density of drilling fluid dramatically reduces, which minimizes the possibility of formation damage and benefits the identification of pay zones. Simultaneous monitoring of pressure and flow rate enables the PCDS-I to accurately detect and deal with several overflow incidents in time. Near-balanced drilling condition is created by the PCDS-I which significantly increases the rate of penetration while preventing the pipe sticking and wellbore collapse, contributing the improvement of operation efficiency. A well using the PCDS-I even set a single bit footage record of 312.88 m and daily footage record of 163 m. No drilling issue is reported in the applications of the PCDS-I.
Successful applications of the PCDS-I demonstrates its technical advantages in solving the issues of offshore drilling. Utilization of this new-type managed pressure drilling equipment dramatically minimizes the potential of well control and ensures the down-hole safety, controls the formation damage and assists pay zone identification, enhances the drilling performance and reduces the non-production time, improves the drilling efficiency and economic benefits.
