Geothermal Wells - Health and Safety Guidelines for Shallow
Part 3: Well Sites
301 General
301.1 This part covers the requirements for the selection and location of well drilling sites.
302 Site Selection
302.1 Before well drilling operations commence notification of the location of the proposed well shall be made to the authority having jurisdiction.
302.2 Site selection should consider geological factors which could affect the stability of the well drilling site and any surface thermal activity in the immediate vicinity of a proposed wellsite.
Note:
(1) Warm and steaming ground may present gas and scalding hazards to well site personnel.
(2) Well sites located over cavernous ground pose a hazard as the ground may collapse exposing hot fluids.
(3) Where near surface temperatures are close to boiling, the removal of overburden or the lowering of ground-water levels could initiate a localised eruption of steam and mud.
303 Site Access
303.1 Reasonable access should be maintained to the well and wellsite for workover and emergency services at all times.
304 Site Location
304.1 The location of a well should comply with the requirements of local authorities and public utilities where applicable.
304.2 A well shall not be enclosed by a building or structure except where ventilation to prevent the accumulation of hazardous gases is ensured and where adequate access to repair and properly abandon the well is maintained.
304.3 The site should have sufficient open surroundings to prevent the accumulation of dangerous gases.
Note: Hazardous areas can be created by shelter belts, solid fences and similar barriers to the free movement of air.
305 Cellars
305.1 Cellars, where required, shall be well ventilated and the depth shall be minimised.
305.2 Cellars shall be adequately drained to minimise the accumulation of water on the cellar floor.
Note: Noxious gases can reach dangerous concentrations in deep cellars due to the lack of natural air movement.
305.3 Wellheads located below ground level shall have a cellar which shall be covered with a protective plate or grill that also enables access for inspection purposes.
306 Site Drainage
306.1 Surface drainage and well design should ensure that no water can pool around the well casings at ground level.
307 Water Supply
307.1 An adequate supply of water shall be available on the site during all drilling operations. The supply shall be adequate for all quenching, drilling, and cementing operations.
308 Well Site Security
308.1 Drilling sites located in public areas should have adequate fencing and signage to discourage the entry of unauthorised personnel.
308.2 Wells located in public areas and exposed to vehicular traffic shall be protected by an appropriate protective barrier to prevent damage to the wellhead.
Part 4: Drilling Practices
401 General
401.1 This part of the Guidelines sets out the minimum standards of drilling practice required for well control, casing, cementing, completion, drilling problems, record keeping and maintenance during the drilling or workover of a shallow geothermal well.
402 Well Control
402.1 Well control equipment shall be used on all drilling and workover operations except those in areas where the known maximum well temperature is less than 90 deg C and there is no measurable wellhead pressure.
402.2 Well control equipment shall be selected to adequately and safely control all anticipated pressures and temperatures in the well.
Note: For low pressure wells, a diverter, designed to contain and redirect all anticipated pressures and flows during drilling operation, may be used, and shall be fitted with a suitably sized and rated full opening valve on the discharge line to enable the discharge from the well to be controlled.
402.3 Discharge lines shall be located so as to discharge in a controlled and safe manner.
402.4 Controls and operating equipment for the well control devices shall consist of suitably sized and rated equipment located a safe distance from the wellhead.
402.5 Well drilling operations shall not commence until there has been assembled on site, with all necessary connections and materials ready for urgent use, sufficient and appropriate equipment for cooling and for sealing the well.
402.6 An adequate supply of water shall be available at the well site to quench the well during drilling and workover operations.
403 Drilling Fluids
403.1 The characteristics of the drilling fluid, the equipment to handle such fluid, and the method of use of the fluid shall be such as to provide adequate control of the maximum subsurface pressures expected to be encountered in drilling the well.
Note: Drilling fluids are required to remove cuttings and formation gas from the well during drilling, to cool and lubricate the bit and drill string, to apply pressure to formation fluids for controlling flow into or out of the well, and to cool the formation — particularly prior to cementing. Various drilling fluids are selected according to reservoir pressures and temperatures and to drilling techniques proposed. Drilling fluids normally used include water, water-based bentonitic muds, aerated water or mud, stiff foam, mist or air.
Photo 9 - An example of a shallow
geothermal drilling rig
Photo 10 - An example of a
blowout preventer for shallow
geothermal wells
403.2 During drilling operations, sufficient reserves of water, drilling fluid, and supplies of drilling fluid materials shall be available at the well site for immediate use.
403.3 The volume of the drilling fluid, and the flow rate, temperature and contents of any returns, should be monitored closely to provide the earliest warning of an uncontrolled flow back of fluids from the reservoir.
Note: A significant gain or loss of total volume which cannot be accounted for (e.g. surface losses, aeration), a total loss of returns, a rapid increase in heat returned to the surface, or formation gas in the returns, may be indicative of a potential flow of formation fluids into the well. The fluids may contain any mix of gas, steam or hot water and initiate an eruption of fluid from the well.
404 Running Casing
404.1 The lengths of all joints of casing, including accessories, shall be measured and recorded.
404.2 All casings should be handled and stored to ensure no damage results to the pipe or threads.
404.3 All casing couplings should be tightened to the manufacturer's torque specifications.
405 Cementing Casing
405.1 All casing strings, except open hole slotted liners, shall be fully cemented into place.
405.2 Casings shall be cemented with a uniform quality cement grout which fills the annular space between the casings, and extends from the shoe to the surface.
Note: An attempt should be made to seal severe loss zones prior to cementing using cement slurry slugs, or loss circulation material additives to enable adequate cementing of the casing.
405.3 Cement should be pumped down the inside of the casing and circulated back to surface up the casing/drillhole or casing/casing annulus.
405.4 The pumping and circulation of cement for casing strings should be uninterrupted.
405.5 Circulation of the cement slurry should cease when uncontaminated cement is circulated out of the drillhole annulus at the surface.
Note: The cementing programme should use materials, and be undertaken in a manner, which is most likely to ensure that the total length of the annulus outside the casing is completely filled with a sound cement which can withstand long-term exposure to geothermal fluids and temperature anticipated in the drilling of the well.
406 Well Completion
406.1 The total length of the drill string in the hole at the time the bit is at the bottom of the hole shall be checked to confirm the final drilled depth. This check should include counting the drill pipe removed and measurement of the bottom hole drill assembly.
406.2 If a liner is run in the well the liner shall extend from the final depth to a minimum of 10 metres above the shoe of the previous cemented casing.
407 Wellhead Installations
407.1 Seal rings or gaskets used in flanged connections shall be clean and free from damage or defects.
407.2 Ring grooves, rings for sealing, studs and bolts shall be uniformly greased before installing the sealing ring and assembling flanges together.
407.3 Flanges shall be pulled together uniformly by progressive tightening of the nuts around the flange systematically such that the flanges are essentially parallel throughout the tightening process.
407.4 When the flanges are fully made up, all nuts shall be fully engaged with the bolts or studs such that there is a short length of bolt or stud protruding from each nut.
407.5 All stud or bolt holes in a flange shall contain an appropriate stud or bolt in order to achieve the full pressure rating of the flange.
407.6 The wellhead and exposed casing should be sandblasted and painted with a high temperature compatible paint system to afford maximum protection against surface corrosion.
407.7 Following well completion and rig removal, a circle of cement measuring a minimum diameter of 0.5 m should be placed around the wellhead, raised and graded to ensure that no surface run-off water can accumulate around the well.
407.8 Where a cellar is constructed, drains from the cellar should be cleared to minimise water accumulation in the cellar floor. The site shall be graded in a manner which will prevent surface run-off water entering and silting up the cellar.
407.9 The rig shall not be released until the well has been left in a safe condition.
408 Record Keeping
408.1 The following information, where applicable, obtained during drilling and completion shall be recorded with respect to date and well identification, and permanently stored for every well.
The following information shall be recorded and kept in a daily log:
(a) The well name, number, and location.
(b) The elevation of the kelly bushing, or rotary table, above mean sea level and above ground level.
(c) For each 24-hour period; the date, the drilling depths at the beginning and end, and distance drilled.
(d) The current diameter of the hole.
(e) The current operation.
(f) The completion data on the final daily drilling log.
(g) The details of any casing operations and any subsequent modifications.
(h) The cementing details, including slurry volumes used.
(i) Downhole measurements, casing surveys, temperature surveys, and any other test or survey carried out.
(j) The record of other operations such as fishing and equipment lost in the hole.
(k) Circulation losses.
(l) Drilling breaks.
(m) Changes in geothermal activity on the surface in the vicinity of the geothermal work.
408.2 The following information, where applicable, shall be recorded and included in a summary report upon completion of the well drilling operations.
(a) The name and address of the well owner and the bore manager.
(b) The well name and number, casing head flange elevation with respect to an established geodesic datum, and location in terms of metre coordinates of a recognised geodesic grid to the nearest half metre.
(c) Description of the work carried out on the well.
(d) The date of commencement of workover or well-drilling operations, or spudding-in of the well, when total depth was reached and when the rig was released.
(e) The total depth reached.
(f) The details of the completed well and wellhead with dimensioned schematic drawing.
(g) The hole sizes and depths.
(h) The casing and liner details including size, weight, grade, thread, and coupling, number of joints, details of slotting, and setting depths.
(i) The casing cementing details including the quantities of materials used.
(j) The details of any equipment left in the hole.
(k) Summary details of wellhead pressures, chemical sampling, downhole measurements, and their interpretations.
(l) The drilling fluids used.
(m) Circulation losses.
(n) Geological description of well lithology and stratigraphy.
409 Equipment Maintenance
409.1 All equipment and structures forming part of the drilling operation shall be subjected to appropriate inspection, lubrication and maintenance as recommended by the equipment manufacturers. A maintenance register shall be kept detailing maintenance required and the maintenance performed.
409.2 During drilling, well control devices, and wellhead components shall be checked daily for damage, leaks of hydraulic fluid and any other aspect which could adversely affect the control of the well.
409.3 Adequate first aid facilities and stocks of materials shall be maintained on site at all times during drilling or workover operations.
410 Personnel Safety and Training
410.1 Prior to the commencement of work, all personnel should be instructed and trained in well control and in the correct and safe use of all equipment and machinery with which they work, and a logbook shall be maintained to record such instruction and training.
410.2 At least one person who has attended a recognised first aid course and holds a current certificate of competency in first aid should be available on site at all times during drilling operations.
410.3 Prior to the commencement of work, personnel should be made aware of the hazards normally associated with drilling together with the hazards associated with hot geothermal fluids.
Note: Instruction should include: testing for CO2 and H2S; well quenching; spontaneous well discharge; and a review of site-specific hazards.
410.4 All personnel on a well site where there is a drilling rig shall wear appropriate personal safety equipment. Additional safety equipment may be required where hazardous materials are being used.
Note: Equipment may include hardhats; goggles; gloves; aprons; wet gear; earplugs/muffs; dust masks, etc.
410.5 Where hazardous gases may be present on the site, gas detectors and breathing escape apparatus shall be available on-site and personnel shall be fully trained in the use this equipment.
