We became aware in early 1981 of a severe problem with casing failures opposite salts in the Little Knife field. A concerted engineering effort was initiated to isolate and to remedy the cause of failures. With the use of a relaxed invert-oil-emulsion drilling fluid and properly designed cementing programs, the problem has been arrested. In the 26 wells drilled in the Little Knife field since initiation of this drilling program, there have been no instances of casing failure.

Some of the most challenging drilling encountered in the Uintab Basin of northeastern Utah occurs in the Altamont and Bluebell Fields (see Figure 4). Drilling costs in the area have been historically high due to such problems as surface water flows, lost circulation, abnormal pressure, hard and abrasive formations, and flows pressure, hard and abrasive formations, and flows of crude oil with high concentrations of paraffin. Through implementation and improvement upon a carefully planned and executed drilling program, drilling costs in the area were reduced by program, drilling costs in the area were reduced by 48%. All wells used in this study were drilled using a fully company owned and operated drilling rig. This paper details the Improvements made in drilling fluids system, hydraulics, bit selection, solids control, cementing practices, and other drilling related parameters pertinent to our drilling success. Introduction The Altamont and Bluebell Fields, located in Duchesne County, Utah, went on production in 1971 and 1968, respectively. Production from the two fields amounts to 8400 BPD (1335 m3 PD) from 330 wells. Figure 1 shows a typical cross-section of the area along with the drilling and casing programs used. k 12-1/4" (31.1 cm) hole is programs used. k 12-1/4" (31.1 cm) hole is drilled to +/- 3000' (914 m) and 9-5/8" (24.4 cm) casing is set to isolate surface water flows and provide adequate kick tolerance. An 8-3/4" (22.2 provide adequate kick tolerance. An 8-3/4" (22.2 cm bit is used to drill out and 7" (17.8 cm) intermediate casing is set a 10,500 - 11,500' (3200 - 3500 m) to isolate weaker zones above and prepare for rapidly rising mud weights in the prepare for rapidly rising mud weights in the Wasatch formation. A 6" (15.2 cm) hole is drilled through the Wasatch and a 5" (12.7 cm) production liner is set. production liner is set. Since commencing the second well on a lease development drilling program in November 1983, eight wells have been drilled and completed in the Altamont/Bluebell Fields (see Table 1). The Dillman 2-28A2 was the first well drilled by the Casper Division in the Bluebell Field since 1975, and was drilled using accepted Altamont/Bluebell drilling practices and technology. The well was drilled to a TD of 14,400' (4389 m) in 95 days at a drill and complete cost of $3.019MM or $209.65/ft (see Figure 2). It was immediately recognized that the development project economics would not support well costs of this magnitude. Due to the rapid draw down of wells in this area, low initial well cost is essential if the wells are to pay out in a reasonable amount of time. A total review of Altamont/Bluebell Fields drilling and completion practices was made with emphasis on reducing the total well cost. Based on available bit records, the average drilling time for a Wasatch well in the Altamont/Bluebell Fields was 60 days prior to February, 1984.

Member SPE-AIME ABSTRACT; Since mid-1981, 36 wells have been cemented in the Williston Basin with a cementing system diametrically opposed to conventional cementing designs used for bonding across massive salt members. Since implementation, along with the use of relaxed invert emulsion oil mud, not one casing problem has arisen in the wells where these systems were used. Introduction The Rocky Mountain region provides a myriad of cementing problems. One of these is cementing massive salt members. This is of particular interest to Gulf in their particular interest to Gulf in their operations in the Williston Basin of North Dakota and Montana where numerous and sometimes severe casing problems have been encountered by Gulf and other operators. The salt intervals of interest in the Williston Basin are the Jurassic Dunham salt, the Triassic Pine salt, the Permian Opeche Evaporite, the Pine salt, the Permian Opeche Evaporite, the interbedded salts of the Mississippian Charles Formation, and the Middle Devonian Prairie Evaporite. Also of interest to the Drilling and Production Engineer is the Cretaceous Dakota Formation which is known for its corrosive waters. Doglegged and/or collapsed casing severe corrosion can arise in wells where any or all of these formations are not isolated from the casing by cement. The solution is to insure a contiguous, uniform cement sheath from the top of the Cretaceous Dakota to below the Ordivician Red River. This solution entailed three areas of engineering endeavor:casing design,drilling fluids, andcement. Only the last of these will be detailed in this paper. DISCUSSION WILLISTON BASIN: The cementing procedures outlined in this paper are followed by Gulf Oil in all paper are followed by Gulf Oil in all Williston Basin drilling. The Little Knife Field of North Dakota is used specifically because this field is where the cementing procedures outlined below were perfected. The little Knife Field is located within the counties of Dunn, McKenzie and Billings in North Dakota. To date, 164 wells have been drilled by Gulf. All but two wells in the field produce from the Mississippian Mission Canyon Formation at +9,750 feet (2,972 meters). Two wells are producing from the Devonian Duperow Formation. Of the 164 wells drilled since November, 1976, 13 wells are temporarily abandoned due to low production, 17 wells are plugged and abandoned due to casing failures, plugged and abandoned due to casing failures, 44 wells have casing problems (doglegs, corrosion or tight spots) but are still producible, and 33 wells are still flowing and have not been entered since completion. This means that 37% of the wells drilled in the field have some casing damage. This number may be as high as 57% when all the flowing wells are equipped to pump. Of the remaining 57 pumping wells with no problems, 17 (30%) have been pumping wells with no problems, 17 (30%) have been drilled with a relaxed invert emulsion mud and cemented with a low salt cement. Three problem areas evolved during the planning, drilling and completion of wells in planning, drilling and completion of wells in the Williston Basin in general and the Little Knife Field in particular. The first problem recognized and addressed was insufficient casing collapse design through salt sections. All casing strings run in the Little Knife Field have been designed with 1 psi/foot (22.6 KPa/m) collapse minimums through all salts encountered and in fact a 1.5 psi/ft collapse (33.9 KPa/m) factor is common across the upper salt members in the Little Knife Field. p. 113