A Novel Approach to Green, Safe and Economic Subsea Hydrotesting

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe King West single well deepwater development is a 2.5 miles, 6" flowline tieback to the existing King system western flowline in water depth of 5,500 ft.The King West Project Team was faced with high costs and complex methods for hydrotesting and tying this into the King subsea system. The conventional BP GoM Projects subsea flowline hydrotest method is to pump seawater or fresh water, pressurize it, and test for any possible leaks. Upon completion, the water is discharged subsea or displaced using nitrogen.For deepwater flowlines, residual water from the hydrotest must be inhibited to prevent hydrate formation during initial well startup. However, the bathymetry of the King West flowline indicated that inhibition by methanol displacement alone could not achieve this and complex nitrogen de-watering would be needed.The Project Team suggested investigating the possibility of using natural hydrate inhibition properties of high salinity inhibited completion brine instead of fresh water for flowline hydrotesting.This novel approach has major benefits. It reduced environmental impact and personnel exposure, procedure complexity, risks in dewatering operations; process upsets and allows the hydrotest fluid to flow back with well fluids through the host facility process then safely discharged. Moreover, the well startup time was reduced by approximately two days.In order to fully understand the hydrate inhibition properties of calcium chloride (CaCl 2 ) brine, several tests were conducted at local labs. These test results showed that using a CaCl 2 brine with a concentration of 11.2 ppg (33.9 wt%) would be best for King West hydrotesting.Eight different hydrate prediction softwares were compared with experimental hydrate formation data for high salinity brine-hydrocarbon systems. Comparisons showed only one prediction software matches the experimental data within a close range.The other key finding observed from the experimental data is that CaCl 2 depression of hydrate formation temperature does not reach a maximum at increased concentrations, instead the hydrate inhibition capability continue to increase with further increase in CaCl 2 concentration.The pressurized crystallization point (PCT) for 11.2 ppg CaCl 2 brine at 15,000 psi was measured as 15 o F, which is well below the seabed temperature for King West flowline.The King West subsea system was successfully hydrotested on May 29-30, 2003 by using 11.2 ppg CaCl 2 brine inhibited with corrosion inhibitor and oxygen scavenger. Production was started with no associated facility upsets, hydrate formation or well downtime.

Predicting Gas Hydrate Equilibria in Multicomponent Systems with a Machine Learning Approach

“…In this study, a total of 1608 data values for binary and multicomponent systems were extracted from various literature studies, which are provided as Supporting Information in Tab. S1 27–76. The complete dataset used for ML consists of hydrate equilibrium conditions, SG, and inhibitor concentrations, which are provided in the Supporting Information.…”