Water Management in Oil and Gas

Question 1

Relation of water and the industry of oil and gas (extraction)

Answer 1

Water is considered a byproduct of oil and gas production, and generally tretaed as a waste for disposal.

Most practices across the sector focus on disposal, rather than beneficial reuse (except for unconventional gas in Australia)

Question 2

Water is everywhere in oil and gas

Answer 2

• Subsurface - groundwater in aquifers (acuiferos)
• Injected to increase yield from wells
• Potable water to provide to workers in remote campus
• water as an indicator of environmental impact
• Stormwater management in refineries/compressors/other facilities

Question 3

What is produced water?

Answer 3

• water produced when oil and gas are extracted from ground
• Measured in bbls. 1BBl=159L
• The largest waste stream in O&G
• Handling depends on composition of produced water (quality), location, quantity and availability of resources.

Question 4

In which principle is based the treatment of water in oil extraction?

Answer 4

Oil is lighter than water - and most water treatment is based on this difference in specific gravity.

Question 5

Why manage water?

Answer 5

• Profitability (rentabilidad)
• Social license to operate
• Regulatory pressures
• Environmental damage is extremely costly

Question 6

Objectives of O&G water management

Answer 6

• treat as little volume as possible (treatment is costly)
• Shift as little volume as possible (pumping is costly)
• Ensure disposal water is appropiate quaility (matching quality of discharge location)
• Sustainable operation, protect existing environment - ensure existing conditions are not modified in any way (flows, contaminants)
• Multi-barrier approach to alleviate process risks

Question 7

Produced water and the Environment

Answer 7

• Environmental impacts of O&G operations are often related to oil spills, but produced water disposal if not managed correctly can cause degradation of soil, alter receiving waterways, and damage ecosystems
• Erosion can be caused through discharging of high volumes of produced water incorrectly
• Much of the potential environmental impacts are subsurface – groundwater cycle

Question 8

Utilising Water Quality to Monitor Environmental Impact

Answer 8

Like many sectors, environmental impacts of O&G operations can be monitored by
monitoring water quality for ‘indicator parameters’

• Baseline monitoring is performed, then changes in parameters are monitored
• Common indicator parameters are TOC, BTEX, Sodium, Electrical Conductivity
• Regulatory bodies often enforce monitoring, and will audit data collection

Question 9

Water in Conventional Oil Production

Answer 9

• Wellhead separation, and skimming
• 1120 – 1600L of water are produced for every bbl of crude oil, on average
• Low initial water production, higher at end
• Injection used to maximise yield from each well – Enhanced Oil Recovery
• Contaminants – oil and grease, BTEX, salts, microorganisms
• Treatment technologies – oil & grease separators, desalination, antiscalant dosing, disinfection

Question 10

Water in Unconventional Oil Production

Answer 10

• Unconventional oil production; oil shales, coal based or bio-mass based liquid supplies
• High volume of water usage associated with field development – fracturing (not much in Australia, largely in USA)
• Produced water has similar contaminants to conventional, but higher suspended solids
• Production profile changes - flatter

Question 11

Water in Conventional Gas

Answer 11

• Lower production volume
• Less controversial than unconventional - no fracturing of aquifers – less controversial,
  lower water demand
• High hydrocarbon concentration than unconventional gas due to presence of oil
• Much different management strategy to unconventional due to different production
  pattern and composition
• Fewer wells, higher pressure, higher production per well
• Water gathering network is much simpler and localised

Question 12

Water in Unconventional Gas

Answer 12

• Unconventional gas – Coal seam gas, coal bed methane, shale gas
• Higher production volume
• Complex, large gathering networks – collecting water from a high number of wells
• Often used in fracturing – particularly USA
• Low hydrocarbon concentration, high salt concentration – influences treatment strategy
• Shallower wells, lower pressure, artifical lift with progressive cavity pump from well inception

Question 13

Treatment Technologies – Oil and Water Separation

Answer 13

• Used in conventional and unconventional oil production
• Range of designs utilised, but most rely on principle of differing specific gravity properties of oil and water to separate
• Separation by gravity, gas flotation, coalescence through demulsifiers, and separation by centrifugal force
• Used in wastewater treatment plants but also to recover oil
• Application in O&G – refinery wastewater treatment, oil recovery

Question 14

Treatment Technologies – Flocculation and Clarification

Answer 14

Flocculation and coagulation is a commonly used treatment process in both
industrial and municipal water treatments;

• Uses a chemical (coagulant) to bind contaminants to a floc, which is then separated from process as wastewater
• Adaptable to a range of contaminants – just need to change the coagulant being used
• Tank design needs to consider settling time
• •Often used in conjunction with media filtration, used for waters with suspended particles
• Application in O&G: wastewater treatment, frac fluid treatment, drilling fluid treatment

Question 15

Treatment Technologies – Reverse Osmosis (desalination)

Answer 15

Energy intensive process used for removing salts;

• High pressure pumps force water molecules through membrane (permeate), leaving salts behind (concentrate);
• Produces concentrate and permeate streams
• Energy intensive due to high pressure pumps
• Application in O&G:
  
  • extracting salts from extracted groundwater to ensure suitable for further disposal,
  • Treatment of groundwater prior to use as potable water

Question 16

CSG Main Principles

Answer 16

• Groundwater needs to be extracted to lower pressure in coal seam and release natural gas, which is extracted via a production annulus of a well
• Water is extracted from aquifers usually 600 – 800m deep, much deeper than drinking water aquifers
• High water production initially using progressive cavity pump, then gas pressure will lift water to surface in small volumes
• Generally water is high in salt in Australia, and Reverse Osmosis is commonly used to extract salts for main production water;
• Drilling water also needs to be treated, as well as frac flow back water
• Water management for CSG is extremely expensive in Australia due to; remote locations, treatment requirements, high construction costs, tight Australian standards and regulatory requirements – far greater than in North America and Municipal treatment in Australia
• Water management can often cause field developments to be uneconomic

Question 17

CSG - Stakeholders

Answer 17

• Both Federal and State regulatory Bodies;
  
  • Approve developments
  • Assess environmental impact statements
  • Issue and monitor license to operate
  • Need to ensure that CSG development will not result in environmental impacts
• Land owners;
  
  • Concerns of how leases are accessed and developments on land
• Internal stakeholders
  
  • shareholders, senior management;
  • Approve developments internally, so need to know that environmental risks are not significant
  • Often harder to convince than regulators – projects need to be sustainable, cost effective, reliable, and of sufficient quality.
• Cultural heritage

Question 18

CSG – A Project Process

Answer 18

1. Reserves identified
2. Reservoir engineers / hydrogeologists determine likely quantity based on Darcy’s law, and then quantity based on indicative samples
3. Gathering network is designed based on quantities, locations, topography, environmental constraints, land access, construction issues
4. Treatment plants designed based on quality, quantity, and likely disposal source
5. Economics assessed, and if economic project is sanctioned
6. Construction phase – large activity in short period, high resource demand to execute
7. Operations phase – monitoring and reporting to regulator
8. Rehabilitation phase – returning site to original condition

Question 19

CSG –Wellhead and Gathering Network Design

Answer 19

Gas / Water Separation

• Gas bubbles out of water and is separated into gas and water pipelines
• Separator sizing based on anticipated production

Gathering Network

• Minimise pipe distances, maximise flexibility
• High point vents in pipelines to remove gas
• Validate design with hydraulic modelling
• Consider operational buffering storages
• Network to have sufficient flexibility to be able to isolate sections and take treatment plants offline with minimal impact on gas production

Question 20

CSG –Water Treatment Plant Design

Answer 20

Treatment Plant Design

• Contaminants and required disposal quality dictate best technology
• Often small amount of water quality data and quantity estimates, so build contingency into design, and flexibility
• Designs are modular and transportable (often containerised) to lower costs associated with onsite construction
• Consider system redundancy, waste, quality, reliability
  
  • Assess all of these against cost

Question 21

CSG – Beneficial Use of Water

Answer 21

One of the requirements of the regulator is to, where possible, use produced water
beneficially (once treated to appropriate quality). This is done through a variety of
ways;

• Irrigation schemes
• Managed aquifer recharge – top up potable water reserves
• Dust suppression and construction uses, which have high demands during project construction phase
• Restoring waterway flows to pre-environmental settlement
• Supply to external farmers
• Approach is often quite expensive, but satisfies regulator and is part of being a good corporate citizen