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.~ • improve the cement bond before the tail cement is pumped into the casing for rotary drilling operations where viscous drilling fluids have caused filter cake build-up; and (d) using wall cleaners or scratchers installed across the pay zone to improve the cement bond if viscous drilling fluid has caused filter cake build-up on the well bore. ~ 3.12.25. Centralizers Centralizers should be run at 15 metres above the top and at the base of every porous formation and in no case at intervals greater than 100 metres. 3.12.26. Lightweight Cement Lightweight cements can be used to protect formations from excessive hydrostatic pressures and potential lost circulation under the following conditions: (a) a sufficient volume of neat tail cement is pumped to place the top of the neat cement at least 50 metres above the uppermost hydrocarbon bearing formation; and (b) the tail cement covering the potential pay zone is equal in quality to the classification of neat cement. 3.12.27. Multi-Stage Cementing Stage cementing tools and techniques shall be used to protect formations from excessive hydrostatic pressures and potential lost circulation when primary cementing fails to or cannot isolate these zones. 3.12.28. Remedial Treatments/Cementing Remedial techniques shall be used to meet design considerations when unconsolidated formations, sloughing shale, lost circulation and other such conditions are encountered and if there is evidence of communication between permeable formations behind a casing string and where hydrostatic communication is suspected between porous formations. 3.12.28.1. Cement Bond Log Where remedial treatments are indicated a cement bond log shall be run prior to a cement squeeze to identify the problem, and after the cement squeeze operation to confirm its effectiveness. The operator shall record and retain on file remedial cementing records including procedures, observations, and pressure test results in full detail. 3.13. Surface Equipment All valves, tubing and casing heads, and tubing and casing spools installed on the wellhead shall comply with API Spec 6A: Valves and wellhead equipment. For solution mining wells valves shall comply with APl 6A or CSA 651-95 Boiler, Pressure Vessel and Pressure Piping Code. Prior to completing the well after the production casing has been set and cemented, the operator shall: (a) install a casing head or spool with at least two valved and bull plugged side outlets to allow pack-off of the production casing and the intermediate casing annulus in the event that insufficient cement was pumped to isolate all main hole porous zones from the surface during the production casing cement job; (b) provide a wellhead to isolate the annulus at the surface or isolate the potential flow of water down hole, if flows of water are possible from outside the intermediate casings; and 19