GB2398297A - Disposal of waste into oil and gas wells - Google Patents

Abstract

A process for disposing of domestic waste into redundant oil and gas wells is disclosed. Initially, different types of waste may be separated on a conveyor system before being shredded to form a granular material. The granular waste may be subsequently mixed with seawater to form a mixture that can be pumped into the well.

Description

Patent Applicationfo; disposal of domestic waste into offshore oil and gas

wells. 2398297

Executive Summary

Recent European Legislation regarding the disposal of waste into landfill sites for the protection of the environment presents the UK local authorities and their European counterparts with a dilemma in sourcing alternative means of disposal.

This application demonstrates a unique solution to the UK authorities through the development of a process to dispose of waste into oil and gas wells that are no longer economically viable offering an alternative to the utilisation of landfill sites and other processes such as incineration that also have levels of environmental impact.

The process not only offers a solution to the UK local authorities and their European counterparts but also to the UK oil and gas industry with the proposition to reduce the cost of decommissioning wells by apportioning an element of the cost of waste disposal towards the cost.

The application is a process that involves the recycling and reduction of waste size, transportation offshore and injection into the redundant oil wells. The process has synergies with other industries and processes and has to be viewed in its cutirety though the philosophy of disposing of domestic waste into oil and gas wells is unique.

To aid clarity supplementary background information on the oil and gas industry, the UK fields and well decommissioning methods has been incorporated within this application. a'

Patent Application.for disposal of domestic waste into offshore oil and gas wells.

1.0 Introduction

Domestic waste management is a growing concern for the European Union with over 2,000 million tonnes of waste produced each year within the European Community and over 40 million tonnes classed as hazardous.

As a result the European Union has implemented the European Directive 99/31/EC (http://www.europa.eu.int/scadplus/leg) aimed at restricting the types of waste deposited in land filled sites and also requires the treatment of waste prior to disposal. This Directive is predominately aimed at reducing the environmental impact land filled sites have on land along with the resulting seepage of toxic discharge into the underground water supply, coupled to this recent research by the Marine and Atmospheric Research in Utrecht has suggested that historical dump sites are now posing a threat to the ozone layer as Methyl Chloroform (MFC) is leaking into the atmosphere (BBC teletext). Within the UK this has had a major impact on the local authorities that are responsible for waste disposal, according to figures from the Department of the Environment, Transport and the Regions 83% of refuse goes into landfills, 9% in incinerators, and just 8% is recycled (http://www.dtlr.gov. uk/statistics/index.htm).

Under the Directive 99/31/EC landfill sites are now subject to taxation and there is now a requirement to source alternative methods to dispose of domestic waste, liquid waste, flammable waste, hospital/clinical waste and lyres. This impact has had major cost implications for the local authorities and consumer including private and commercial users nationwide.

On average domestic waste is made up of a number of components (Reference figure 1) and ideally a high percentage of the waste could be recycled, however in reality though the separation of the waste at the household is feasible transportation of the separated waste would require an increase in transportation which ultimately would cause further harm to the environment through pollution and traffic congestion.

As an example of the scale of the problem Aberdeen city council clear 65, 000 domestic waste bins per week contributing to over 140,000 tons of domestic waste per annum and the aim of the council is to reduce the amount of waste generated by Aberdeen households and businesses and to find alternative methods for dealing with refuse to minimise damage to the environment (http://www.aberdeencity.gov. uk/acc/YourCouncil/Departments).

The Council is committed to targets including: Diverting the amount of household waste going to landfill by 40% by 2005.

Reducing household waste by 1% per year.

À Recycling and composting a minimum of 25% of household waste by 2005.

À Ensuring an integrated kerbside collection system for garden and green waste by 2005.

It is envisaged that due to Aberdeen's geographical location within the UK and access to the Oil and Gas Industry the project will commence within this area also enabling the Highlands and Islands and Aberdeenshire councils to access the service.

With the requirement to deliver a solution for this waste problem and to overcome the commercial and environment barriers it is proposed to patent a waste disposal method to protect the concept and process of recycling a percentage of the domestic waste and disposing of remaining waste into used oil and gas wells that are no longer commercially viable to the oil and gas operator. This method would potentially also bring benefits to the oil and gas industry by reducing the costs of decommissioning wells by apportioning a percentage of the overall cost to the waste disposal process.

It is proposed that the patented process will interface with the current oil and gas well decommissioning method though due to the historical nature of well decommissioning this element does not form part of the application. As elements of the patent application process involves operations that are currently utilised in other industry's it is proposed that the application cannot be isolated to a singular stage but the patent application has to be view in it's entirety.

2.0 Domestic waste disposal The patent application process (Reference Appendix I) commences at the delivery of the waste product to a designated factory; it is proposed that refuse trunks would either deliver the waste directly to the facility after uplift from the residential areas in and around Aberdeen or from the local authority's land fill site. The waste would then complete a number of stages encompassing: Stage One - Waste Separation and Recycling The waste will be off loaded through a funnel system and to a conveyor system (Reference figure 2), the conveyor system will be a sliderbed belt conveyor where the belt slides directly on the frame section to give maximum rigidity and loading capacity.

With the waste loaded onto the conveyor system the waste will be manually segregated with bags split open to expose the contents for the removal of the majority of tin cans and bottles.

Personnel will be tasked with the removal of specific recyclable waste and will place these on a smaller conveyance system into receptacles for eventual uplift to recycling plants. To reduce manual operations metallic objects such as tin cans etc will be removed by a magnetic process suspended above the conveyor system To prevent chemicals such as oils and detergents entering drains and eventually rivers the conveyor will be erected over a closed drain system and the disposal of the contents will eventually be included in the process.

Stage Two - F*st Stage Shredder At the end of the conveyor system the waste enters the first stage shredder where the waste is reduced to segments of 20mm, the shredder will be capable of handling materials such as paper, wood and a limited number of glass and steel items (Reference figure 3). To prevent shock to the equipment in the event that a nonshreddable material enters the machinery the shredder will be fitted with an auto reverse linked to the conveyor system to temporary halt the input of waste. Coupled to this system will be an advanced level of shock load protection featuring a torque limiting coupling between the motor and gear reducer where the coupling slips to prevent the torque being transmitted to the shredder drive train protecting the system from potential damage.

Stage Three - Second Stage Shredder The shredded material would then exit the first stage shredder directly onto a side skirted conveyor system (Reference figure 4) to retain all the particles, this conveyor feeds the second stage shredder. The second stage shredder will be of a similar design to the first stage shredder but will be able to reduce the 20mm waste particles down to +1- i/ mm granules equivalent to grains of sand. as

Stage Four - Packaging and Storage On completion of stage 3 the granular waste is transported via a further side skirted conveyor belt to a sack placer, at this stage the waste is transferred into plastic sacks. The proposed sack placer (Reference Figure 5) is a belt feed sack magazine with a holding capacity of up to 300 sacks. It will be suitable to present 10kg to 50kg size plastic sacks automatically delivering up to a speed of up to 15 bags per minute, loading and sealing the sacks for hygienic purposes and storage purposes until the offshore intervention stage is ready.

-I -

Stage Five - Well Preparation After the identification of a suitable subsea field or particular subsea well that is no longer commercially viable to the operator the subsea Christmas tree will be prepared to accept waste. Utilising a vessel such as the WOUKL Seawell (Reference fig 12) that has a motion compensated derrick system the vessel will sail to location and remove the Subsea tree cap and install an adapted tree running tool.

Upon arrival at the site vessel will verify the Christmas tree valve positions using a Remote Observation Vehicle (ROY) and install guidewires onto the tree's flowbase guide posts. The guidewires act as a means to guide equipment to/from surface onto the Christmas tree.

From the vessel the will be unlocked hydraulically and utilizing the vessels derrick lift wire the cap will be recovered to surface. With the tree cap removed this will isolate the hydraulic control of the tree from the host platform and allows vertical access into the wellbore with a tree running tool (TRT).

A modified Tree Running Tool (TRT) will then be deployed and hydraulically latched onto the tree in a process that is similar to the tree cap removal. The TRT has the same profile as the tree cap with a through bore to which the hydraulic connectors will be assembled via a flanged crossover (Reference figure 6). These hydraulic connectors enable the installation of a Coflexip hose at a later date to inject the waste into the wells reservoir, the TRT also has an interface for the connection of a hydraulic stabplate to control the opening and closing of the tree valves. On completion of a series of pressure tests to ensure that the TRT is pressure retaining and functioning correctly a plug will be install by ROV into the hydraulic connectors and the vessel will leave location.

Stage Six Offshore Waste Disposal On completion of stage five the well is in a position to accept waste, the stored waste will be then be transported offshore using a suitably equipped dynamically position (DP) offshore supply vessel (Reference figure 7) and mobilised in harbour along with batch mixers, pump units and Coflexip hoses to pump the waste into the well.

The vessel on completion of mobilization will transit to a predetermined location and enter the field, as the vessel is classed as a DP vessel this requires no anchors to maintain position but relies on a computerized propulsion system to maintain position over a predetermined location. On completion of DP trials the vessel will position itself over a subsea well and access the well.

If applicable the host oil and gas platform will verify that the well is isolated and the production Bowline has been depressurised a remote observation vehicle will confirm the subsea tree valves are in the closed position.

The vessel will deploy a control umbilical over the side of the vessel and interface the umbilical with the TRT utilizing the vessels ROV, tree control will be established and any pressure build up under the TRT hydraulic connector plug will be vented. The plug will be recovered to surface and the Coflexip hose (Reference figure 8) over the side with suffice length to compensate for wave motion and vessel excursion. At depth the ROV will interface the hose to the TRT hydraulic connector, as well as the termination point the TRT connector and umbilical interface act as a release mechanism enable the umbilical and Coflexip hose to be released in the event of an emergency (Reference Figures 9 & 10). Non return valves- within the Coflexip and umbilical retain any fluid within the hoses protecting against release of waste and hydraulic fluid into the sea.

Surface connections will be made between the batch mixer, pump and Coflexip hose and all connections will be pressure tested to ensure integrity from surface to the valves on the Subsea Christmas tree.

Stage Seven - Wellbore Disposal On completion of the testing the well will be opened and filtered seawater will be injected into the well through the production tubing perforation to establish injection rates and infectivity if the formation has compressed. On completion waste will be mixed in the batch mixer to a ratio of 12 litres of filtered seawater to lkg of waste, the by product from the oil trap will also be included within the process and subject to the type of formation a polymer maybe added and the ratios adjusted to add injection of the waste.

The waste would then be pumped under pressure and squeezed into the formation on completion in a continuous process at rates of up to 16 barrels a minute. On completion of the operation the Coflexip hose would be flushed with filter seawater into the wellbore to ensure all waste has been removed. Once a sufficient volume has been displaced the Christmas tree valves will be closed in and the Coflexip hose released and recovered to surface. The TRT hydraulic connector plug will be installed and pressure tested and the control umbilical will be released from the TRT and recovered to surface, the ROV will complete a survey of the tree and the vessel will depart to harbour for the collection of a further batch of waste for disposal.

On completion of a number of waste disposal interventions and with the wells reservoir at capacity the TRT will be removed, refurbished and installed on another well for continuation of the process. With disposal operations completed on the well the well can now be decommissioned as outlined in Section 4 of this proposal.

Synopsis As an example of the volumes that can be disposed of in a singular well a typical subsea well in the Central North Sea will produce over 5,000 Barrels of oil (BOB) per day, averaging 5,000 over a 10-year period this would equate to 18,250,000 barrels of oil. Ace

Using Aberdeen's annual waste figure of 140,000 Tonnes and to meet Aberdeen's aims of diverting 40% of their waste from landfill sites this would equate to 56,000 Tonnes of waste, after recycling of 15% of the waste this would leave 47,600 Tonnes for disposal.

The waste would after onshore processing have similar characteristics as a 50/50 sand/cement mix in terms of weight and volume and using this ratio this would equate to 166,208 barrels of waste, processed with seawater the total volume would equate to 3,759,056 barrels of fluid for injection. In essence one singular well has sufficient capacity to meet the requirements of Aberdeen in diverting 40% of their waste from landfill sites for the next 4 years.

3.0 Oil and Gas fields within the UK

Development of the oil and gas industry commenced in the mid 1960s with gas discoveries in the Southern North Sea (SNS) sector followed by oil production in the early 1970s in the Central North Sea (CNS) sector (http://www.oilandgas.org.uk/issues/storyofoil).

Since the early 1970s the UK has been produced over 29 billion barrels of oil, annually producing 2 million barrels of oil per day in 2001 (Oil and Gas Index), this is produced from over 209 oil and gas fields in the UK sectors and within and surrounding these fields there are over 650 subsea wells. It is estimated that there are still over 30 million barrels of reserves still to be extracted from the UK sectors and it is assumed that due to their low CAPEX/OPEX the majority of new developments will be subsea wells.

Geographically the United Kingdom Continental Shelf (UKCS) is divided into five regions including the Southern, Central and Northern North Sea, the Irish Sea and the West of Shetland basin. The majority of the Subsea wells are located in the Central North Sea that is North East of Aberdeen with further major subsea fields in the West of Shetland basin (Reference Appendix II).

Around the Northern and Central sector oil source rock is buried in a deep rift valley and oil is formed at depths of 3 to 4 km below the seabed, in the Southern sector coal-bearing rocks formed the floor of a basin that filled with younger sediments to form the gas fields. Oilfields and gas fields are areas where hydrocarbons have become trapped in permeable reservoir rocks such as porous sandstone or fractured limestone, over millions of years these trapped hydrocarbons have become naturally pressurized with the hydrocarbons are retained by a layer of capped rock (Reference Figure 12).

After discovery and development of these fields the reservoir pressure will naturally deplete as the hydrocarbons are extracted, to aid lifting of the hydrocarbons processes such as gas lift and water injection is utilized to aid the extraction of the oil. Once the well or field becomes uneconomical to operate due to falling production rates then the field is ready for decommissioning and it is at this stage the waste disposal process commences. il

4.0 Decommissioning of Subsea Wells Subsea well decommissioning can be accomplished by a number of methods including the utilisation of a drilling rig to pull the production tubing or the preferred cost effective method of using a mono hulled vessel with a remote well control system known as a Subsea Intervention Lubricator (S.I.L) (Reference fig 13) For the disposal of waste it is envisaged that live depleted production and injection wells will be selected and waste disposed of prior to the utilization of the mono hull vessel and Subsea Intervention Lubricator. The S.I.L is a pressure retaining well control package that allows vertical access into a live well under pressure to run slickline and electric line wireline tools, in the case of slickline these are predominately mechanical tools and with electric line these tools can either be logging tools or perforating guns to shoot holes in the production tubing at the required depth. In

Production Well Decommissioning To enter a subsea production well for decomnnissioning operations the S.I.L (Reference Appendix II) is configured with a crossover adaptor spool between the S.I.L and Tree running tool (TRT) that allows vertical access to the production bore and porting to the annulus bore.

Once the S.I.L has been deployed and tested on the subsea production well, 2" flexible hoses are deployed from surface and latched into the crossover via hydraulic connectors connected to well control hydraulic valves. The decommissioning operation encompasses a number of steps including: À Conduct slickline drift run - This involves lowering a tool down the production tubing to a predetermined ensure there is no blockages or restrictions.

À Bullhead seawater to tubing - This involves pumping seawater down the 2" flexible lines into the production tubing and into the formation to clear any hydrocarbons from the production bore.

À Punch tubing above packer - Electric line perforation guns are deployed into the production bore and holes shot through into the annulus to create a circulation path À Set bridge plug - Electric line tool is deployed into the hole and a plug inflated using well bore fluids inside the production bore to place the cement plug on top À Squeeze cement - Pump sufficient volume of cement to fill production tubing and annulus À Wait on cement and pressure test plug - Testing plug ensure plug has set and will hold pressure À Punch tubing in upper tubing at predetermined area - Access for second cement plug À Squeeze cement - Install second plug À Wait on cement and pressure test plug - Testing plug ensure plug has set and will hold pressure À Disconnect Bowlines and recover tree - Remove all flowlines/umbilicals from tree to host platform, hydraulically unlock the tree from the flow base À Cut production tubing below hanger and recover Using electric line severe production tubing with a chemical cutter and recover tubing to surface À Cut wellhead Is feet below seabed and recover - Install shaped explosive charge and detonate, recover tubing and flow base to surface For details of a typical subsea well completion and the phase of decommission please refer to Appendix III.

5.0 Environment and future issues Though the proposal is due to be piloted in Aberdeen it is envisaged that this will become a nationwide business with locations on the North East coast of England and East Anglia to handle the waste from around the UK.

From the outset environmental awareness will be paramount identifying a central location near to the city and the harbour to reduce traffic and road congestion in and around the plant.

The plant will have it's own extractor system to ensure dust from the process does not enter the atmosphere and also to protect the staff during the operation.

Future plants will have an emphasis on energy efficiency and the plants that require infrastructure to receive waste nationally will be placed near rail links to reduce road haulage and to reduce harm to the environment.

Ultimately it is envisaged not to limit the waste disposal to subsea wells but also in the future develop a solution for platform wells by utilizing existing infrastructure such as pipelines (Reference Appendix I) to pump the waste offshore and into the wells eliminating the requirement for offshore transportation by vessel.

6.0 Summary

The patent application is for a unique process and has to be view in it's entirety due the utilisation of other processes already used in other industry's, however the benefits are not singular to one business sector but offer the UK local authority's an alternative disposal method within the confines of the latest European legislation and assists the oil and gas operators with their decommissioning costs.

Well capacity is not an issue as the UKCS is a mature province with the larger oil and gas operators such as BP (Aberdeen Press and Journal) now looking to divest their interests to smaller operators who can operate these fields profitably with their lower costs base. However the liability for the decommissioning of these wells and structure still remain with the original license holder and with the emphasis on cost reduction the proposal to utilise these wells for waste disposal will not only create another business segment to the industry but also aid the operator in reducing their decommissioning costs by proportioning the cost of decommissioning across other business segments.

The proposed patent process will reduce decommissioning cost to the oil and gas industry operator and solve the problem of waste disposal in landfill sites around the UK and potentially Europe with a solution to safely dispose of waste alleviating the concerns surrounding landfill sites such as contamination of underground water tables and airborne pollution.

Though the proposal is due to be piloted in Aberdeen it is envisaged that this will become a nationwide business with locations on the North East coast of England and East Anglia to handle the waste from around the UK. Environmental awareness will be paramount in the operation with the utilization of rail links to these plants and processes to recycle higher percentages of the waste. Ultimately it is envisaged not to limit the waste disposal to subsea wells but also in the future develop a solution for platform wells to access the large reservoirs under these structures.

This process will place the UK at the forefront of waste disposal creating a completely new aspect to the waste disposal and oil and gas industry, it will create jobs and creating an effective and environmentally astute method for dealing with the problem of waste disposal while protect the environment. /5

List of Table and Figures

Chapter 1 Introduction

Figure 1 Graph indicating contents of average household waste Page 1 Chapter 2 Patent Application Process Figure 2 Photograph of conveyance system Page 3 Figure 3 Photograph of First stage shredder Page 4 Figure 4 Photograph and graphic of second stage shredder and Conveyance system Page 4 Figure 5 Photograph of sack placer Page 5 Figure 6 Drawing of Subsea Christmas tree with TRT installed Page 6 Figure 7 Photograph of dynarrucally positioned support vessel Page 7 Figure 8 Photograph of Coflexip hose reeler Page 7 Figure 9 Photograph of Coflexip hose interface Page 8 Figure 10 Photograph of hydraulic connectors Page 8 Figure l l Graphic of Trapped hydrocarbons within a formation Page 10 Figure 12 Graphic of Mono hull vessel with subsea intervention Equipment on a subsea well Page 11 Index of Appendix's Appendix I Schematic graph demonstrating processes and patent application Appendix II Geographical location of oil and gas fields in the UK Northern, Southern And Central North Sea.

Appendix III Typical well schematic demonstrating decommissioning sequence! Abbreviations BP British Petroleum BBC British Broadcasting Corporation BOE Barrels of Oil Equivalent CAPEX Capital Expenditure CNS Central North Sea DP Dynamically Positioned EC European community MFC Methyl Chloroform mm Millimetres OPEX Operational Expenditure ROV Remote Observation Vehicle S.l.L Subsea Intervention Lubricator SNS Southern North Sea TRT Tree Running Tools UK United Kingdom UKCS United Kingdom Continental Shelf

Claims (4)

1. A unique process to utilise redundant oil/gas wells to dispose of domestic waste in place of utilising landfill sites or incinerators

2. A process that relies on no new technology

3. A process that utilises existing infrastructure and known techniques

4. A process herein described and illustrated in chapter 2 pages 5 to pages 10 with subsequent information included for clarity À À À À À. À À. À À A. À.. À. À À. Àe À À In. À À À À. À. Iq