AU2001100189A4 - A system for loading, unloading and partial unloading of ballast for offshore oil and gas drilling and production platforms - Google Patents

Description

A System for Loading, Unloading and Partial Unloading of Ballast for Offshore Oil and Gas Drilling and Production Platforms.

The present invention overcomes the following problems associated with the current technology: 1. High Density Pumping (current technology) involves using crushed and ground iron ore (magnetite and/or haematite) being pumped at a high density (90% solids to 10% water). The high density is used to minimise the quantity of excess water released when ballasting. The released water is minimal and does not contain fine solids which may cause contamination of the surrounding ocean. The high density method requires the use of high pressure positive displacement pumps mounted in a separate vessel to the vessel delivering the ballast. The ballast is transferred from the delivery vessel by conveyor into the separate pumping vessel. The ballast is loaded into the transfer pumping system by mechanical front end loader.

The current method has the following technical limitations: a) The high density pumping system requires high pressure positive displacement pumping units. These pumps have a limited capacity and limited throughput. The time for ballasting is approximately double the optimum time to satisfy the narrow safe weather window for offshore ballasting.

b) The transfer pumping system requires high pumping energy to pump the resulting high density slurry.

c) The ballast material, crushed or ground iron ore, is difficult or impossible to recover for unloading or partial unloading of the ballast at a future date.

2. Low density pumping (current technology) to load the crushed or ground iron ore as a low density pumping operation involves the forming of a low density solids by weight and 80-90% water. The excess water to be released to the ocean during ballast loading presents a high probability of fines solids being released into the ocean causing pollution.

The low density method has the following technical limitations: a) The high decant water created during ballasting may contain fine solids that contaminate the surrounding ocean.

b) The crushed iron ore is difficult to unload or partially unload in the future.

The embodiment of the present invention for loading of the ballast is shown schematically in Figure 1. The major components and process are: The ironsands are transported to the offshore drilling and production floating platform by bulk ore carrier Prior to loading the bulk carrier ships, the holds are equipped with fixed FID units ("submerged fluid induction device for transport of particulate solids" Australian Patent No. 3472089) and jet pump The following pump equipment, seawater supply pump seawater feed tanks seawater motivation pump constant density sump and centrifugal transfer pump are mounted on the ore carrier Two of sets of items 4, 5, 6, 7 and 8 are installed. Each set pumps ballast to opposite ballast tanks on the platform.

The discharge of the centrifugal transfer pump is connected to the fixed loading pipe (10) by floating hose prior to the commencement of ballasting the platform Each ballast tank (12) has FID units and jet pump (13) installed in the base of the tank (12).

Seawater supply pump delivers seawater into water feed tank Seawater motive water pump commences operation feeding high pressure seawater to the FID unit and jet pump The FID unit and jet pump fluidise the surrounding ironsands in the hold and pump the fluidised ironsands to constant density sump and the excess water in the recovered ironsands slurry overflows the constant density sump into overflow drain The excess seawater is discharged from overflow drain (14) to the seawater feed tank The constant density sump discharges to the suction of the centrifugal transfer pump at an ironsands concentration in the order of 50 to solids. The centrifugal transfer pump pumps ironsands slurry through floating hose into the fixed loading pipe (10) on the drilling and loading platform. The ironsand slurry is delivered by pipe (10) to discharge in the ballast tank (12).

In ballast tank (12) the ironsands settle and the excess clear decant water is discharged from the top of the ballast tank (12) and returned to the sea via decant pipe The embodiment of the present invention for partial unloading and total unloading of the ballast is shown schematically in Figure 2. The major components and process are: The FID units and jet pump are pre installed in ballast tank prior to loading of ironsands ballast Seawater supply pump and centrifugal booster pump are installed on the floating drilling and production platform The seawater supply pump supplies seawater under pressure to FID units and jet pump The ironsands ballast surrounding the FID units is fluidised and transferred to the jet pump. The jet pump delivers ironsand/seawater slurry to the suction of the hydraulically operated centrifugal booster pump Booster pump pumps ironsand slurry to fixed riser pipe and thence to centrifugal booster pump mounted on the floating drilling and production platform The centrifugal booster pump boosts the ironsands/seawater slurry pressure and pumps the ironsands/seawater slurry through floating delivery hose (10) into the hold (11) of bulk ore carrier The recovered ironsands settle in hold (11) and the excess clear water is decanted from the hold (11) via overflow pipe (13).

A flow meter and density meter measure the quantity of ironsands removed from the ballast tank.