R655-1-5. Injection Wells

  Unless the Division approves an alternative method of disposal, all fluids derived from the geothermal resources must be reinjected into the same reservoir from which the fluids were produced.

  5.1 Construction: The owner or operator of a proposed injection well or series of injection wells shall provide the Division with information it deems necessary for evaluation of the impact of injection on the geothermal reservoir and other natural resources. Information shall include the items listed for a plan of operations as per Section 2.1.2 of this section (R655-1), existing reservoir conditions, method of injection, source of injection fluid, estimates of daily amount of material medium to be injected, zones or formations affected, description of the effects of injection on such factors as potable water, seismicity, and local tectonic conditions, proposed downhole and surface injection equipment and metering facilities with capacity, design capabilities, and design safety factors in sufficient detail to enable adequate environmental analysis including construction and engineering design plans, proposed injectivity surveys, seismic surveys, seismic monitoring, and other means to monitor injection, and analysis of fluid to be injected and of the fluid from the intended zone of the injection, if available. The bonding for an injection well is the same as those required for an exploratory well or production well.

  5.2 Convert to Injection Well: An owner or operator planning to convert an existing well to an injection well, even if there will be no change to the mechanical condition, must submit an injection well conversion plan with the Division and the Division must approve the plan before injection is commenced.

  5.3 Surveillance:

  5.3.1 When an operator or owner proposes to drill or modify an injection well or convert a well to an injection well, he shall be required to demonstrate to the Division by means of internal and external tests that the casing and annular cement seals have complete mechanical integrity. These tests shall be conducted in a method approved by the Division as proposed in the injection well plan of operations. In the case of the annular cement seal survey for a new or converted injection well, the owner or operator shall make sufficient surveys within thirty days after injection is started into a well to prove that all the injected fluid is confined to the intended zone of injection.

  5.3.2 On a continuing basis and in order to establish that all injected water is confined to the intended zone of injection, mechanical integrity surveys on the well casing and annular cement seals shall be made at least every five years or more often if necessary on a well-to-well basis. The Division must be notified in writing with a testing plan for each injection well at least three weeks before mechanical integrity testing commences. Specific internal and external mechanical integrity tests shall be proposed in the testing plan and must conform to the most current industry and regulatory standards for geothermal injection well mechanical integrity testing. The Division shall approve each testing plan and issue a written notice to proceed with testing approval to the operator prior to commencing. A mechanical integrity testing plan shall be submitted by the owner or operator to the Division for approval prior to each testing cycle. The Division shall be notified 48 hours in advance of surveys in order that a representative may be present if deemed necessary. If the operator can substantiate by existing data that these tests are not necessary, then, after review of the data, the State Engineer may grant a waiver exempting the operator from the tests.

  5.3.3 Injection wells shall be monitored to ensure that there is no escape of geothermal fluids from the casings or through the annular space between casings and open hole except in the zone for which injection is permitted. Monitoring required by the Division may include gauging pressure between casings, periodic testing for casing leaks, surveys to detect movement of fluid in adjacent rock formations, cement bond logs, temperature measurements, analysis of water chemistry, special wellhead equipment or other methods employed by industry to monitor re-injection operations.

  5.3.4 After a well has been placed into injection, the injection well site will be visited periodically by Division personnel. The operator or owner will be notified of any necessary remedial work. Unless modified by the State Engineer, this work must be performed within ninety days of approval for the injection well, or approval for the injection well issued by the Division will be rescinded.

  5.3.5 Injection pressures shall be recorded and compared with the pressures reported on the monthly injection reports. Any discrepancies shall be rectified immediately by the operator. A graph of pressures and rates versus time shall be maintained by the operator. Reasons for anomalies shall be promptly ascertained. If these reasons are such that it appears damage is being done, approval by the Division may be rescinded, and injection shall cease.

  5.3.6 The pressure for injection at the wellhead of an injection well must not exceed that which is calculated to initiate new fractures or propagate existing fractures in the zone for injection or the confining formation between the zone of injection and underground sources of drinking water. The operator shall calculate the maximum injection pressure based upon industry standards and submit those to the Division for approval.

  5.3.7 The chemical, physical, and biological nature of the injected fluid must be analyzed with sufficient frequency to yield representative data on its characteristics. When requested by the Division, or at any time the injected fluid is modified, a new analysis shall be made and the results sent to the Division.