Section 20 AAC 25.033 - Primary well control for drilling: drilling fluid program and drilling fluid system(a) A drilling operation must be equipped with a drilling fluid system meeting the requirements of this section, unless the commission determines that a drilling fluid system is not necessary for primary well control. The operator shall submit with an application for a Permit to Drill (Form 10-401) a proposed drilling fluid program and a diagram with a list of equipment for a drilling fluid system designed to prevent the loss of primary well control. The drilling fluid system must be designed to maintain the wellbore in overbalanced condition except as otherwise provided under (i) of this section. A drilling operation is also subject to the requirements of 20 AAC 25.527.(b) A drilling fluid program and drilling fluid system intended to maintain the wellbore in overbalanced condition must be designed to provide and maintain(1) a drilling fluid(A) of sufficient density to overbalance the pressure of uncased formations penetrated; and(B) with rheological properties designed to (i) minimize the potential of a hydrostatic pressure surge or swab when the drilling assembly is run into or pulled out of the wellbore; and(ii) enhance the drop-out of solids and the escape of entrained gas; and(2) a volumetric capacity for drilling fluid reserves adequate for the volume of the wellbore, based on known or anticipated drilling conditions to be encountered, rig storage capacity, weather conditions, and estimated time for delivery.(c) A drilling fluid system intended to maintain the wellbore in overbalanced condition must include (1) a recording drilling fluid pit level indicator with both visual and audible warning devices located in the immediate area of the driller's station;(2) a drilling fluid measuring system or trip tank for accurately determining drilling fluid volumes required to fill the wellbore on trips;(3) a drilling fluid flow sensor with a readout convenient to the driller's station to enable the operator to determine whether drilling fluid returns equal drilling fluid pump discharge rates;(4) equipment to keep the drilling mud conditioned as appropriate for the drilling operation being conducted; and(5) methane and hydrogen sulfide detection equipment as required by 20 AAC 25.066.(d) Drilling fluid testing equipment must be on the drill site at all times. Tests to determine drilling fluid density and viscosity must be performed once each tour, or more frequently if conditions warrant.(e) To ensure that primary well control is effectively maintained, the following practices must be employed in rotary drilling rig operations when tripping the drilling assembly out of the wellbore:(1) the drilling fluid within the wellbore must be in balance and conditioned to maintain drilling fluid properties within close tolerance to the properties necessary for well control;(2) the flow nipple or trip tank must be visually observed to ensure that there is no indication of formation fluid influx;(3) the wellbore must be kept full of drilling fluid at all times;(4) the annulus must be filled with fluid (A) each time that five stands of drill pipe have been removed from the wellbore; and(B) more frequently than required in (A) of this paragraph, if necessary to prevent the hydrostatic pressure from dropping by 75 psi or more;(5) the volume of drilling fluid required to keep the wellbore full while tripping the drilling assembly out of the wellbore must be measured and recorded on the daily drilling report or trip sheet.(f) Additional requirements that apply to exploratory and stratigraphic test wells are as follows: (1) the operator shall include with an application for a Permit to Drill a tabulation that sets out the depths of predicted abnormally geo-pressured strata;(2) if the operator has geophysical data from the area, the operator shall include with an application for a Permit to Drill a seismic velocity analysis constrained by germane well data to predict the potential of encountering abnormally geo-pressured strata, with the analysis displayed by plotting interval transit time versus depth; as the commission considers necessary to evaluate the potential for a well control problem, the commission will require a review from the operator of the velocity analysis and of the plot of interval transit time versus depth;(3) if the operator does not have geophysical data from the area, the operator shall include with an application for a Permit to Drill an analysis of germane well data to predict the potential of encountering abnormally geo-pressured strata;(4) a drilling fluid monitoring unit must be used and continuously observed during drilling rig operations, including tripping, to monitor and record(A) gas entrained in the drilling fluid;(B) drilling fluid density;(C) drilling fluid salinity;(D) the rate of penetration; and(E) hydrogen sulfide, as required by 20 AAC 25.065;(5) means for communication between the drilling fluid monitoring unit and the drill rig floor must be installed and maintained in working condition while open hole operations are taking place, and drill rig floor personnel must be notified immediately if excursions from normal trends occur for any of the parameters set out in (4) of this subsection.(g) If drilling an exploratory or stratigraphic test well, or if drilling a development or service well while known hydrocarbon-bearing strata are exposed to open hole, the operator shall take a drilling fluid return sample and test the sample to determine density just before tripping the drill pipe. Density test results must be recorded as required by 20 AAC 25.070(1). If the density is less than that of the drilling fluid being pumped down the drilling assembly, the drilling fluid must be circulated and conditioned until a close tolerance of the properties of the return drilling fluid with the input drilling fluid is achieved.(h) If formation competence at the structural casing setting depth is not adequate to permit circulation of drilling fluids while drilling the conductor hole, a program that provides for safety in that drilling operation must be described and submitted to the commission for approval. This program must be supported by pertinent information including seismic and geologic data, water depth, drilling fluid hydrostatic pressure, and a contingency plan for moving off location.(i) The commission will approve underbalanced drilling operations and associated equipment changes if the commission determines that underbalanced drilling operations can be performed without loss of well control. A request for underbalanced drilling must include a description of all equipment and procedures to ensure proper containment of formation and return fluids.(j) Upon request by the operator, the commission will, in its discretion, approve a waiver of the requirements of (c) - (g) of this section if the alternative drilling fluid program and drilling fluid system meet the design criteria of (b) of this section and the corresponding equipment and procedures are at least equally effective in preventing the loss of primary well control.Eff. 4/2/86, Register 97; am 11/7/99, Register 152