Drilling Techniques Improve Success in Drilling and Casing Deep Overthrust Belt Salt
- K.W. Unger (Amoco Production Co.) | D.C. Howard (Amoco Production Co.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling Engineering
- Publication Date
- June 1986
- Document Type
- Journal Paper
- 183 - 192
- 1986. Society of Petroleum Engineers
- 1.4.1 BHA Design, 5.3.2 Multiphase Flow, 5.1.2 Faults and Fracture Characterisation, 1.6 Drilling Operations, 1.10 Drilling Equipment, 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 1.11 Drilling Fluids and Materials, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 1.14.3 Cement Formulation (Chemistry, Properties), 1.14.1 Casing Design, 5.5.2 Core Analysis, 1.2.2 Geomechanics, 1.6.1 Drilling Operation Management, 1.12.6 Drilling Data Management and Standards, 3 Production and Well Operations, 1.6.9 Coring, Fishing, 1.1.6 Hole Openers & Under-reamers, 1.14 Casing and Cementing
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Summary. One of the most challenging drilling problems encountered in the Western Overthrust belt occurs in the deep Jurassic Preuss salt. A history of lost holes caused by stuck drillstrings, stuck casing, and collapsed casing plagues operators in the Wyoming/Utah Overthrust belt. An ongoing engineering study is being conducted to identify the problem salt-drilling areas and to solve the associated drilling and casing-collapse problems. In the first part of this study, completed in June 1983, salt-drilling problems were studied in the Anschutz Ranch East field. Problem intervals problems were studied in the Anschutz Ranch East field. Problem intervals within the salt section were identified, and unique salt-drilling techniques were developed. As a result of implementation of the salt-drilling techniques, salt-drilling success in Anschutz Ranch East has improved substantially. Included in this study are an evaluation and recommendations for mud systems, bottomhole assemblies (BHA's), drilling parameters, and caliper logging through the salt interval. Casing collapse caused by nonuniform loading is discussed, and preventive measures are recommended.
Since its discovery in 1979, the Anschutz Ranch East field, located on the northwestern-Utah/ southwestern-Wyoming border in the western Overthrust belt, has undergone extensive developmental drilling. As with other deep Jurassic Nugget fields in the Overthrust belt, one of the most difficult drilling intervals is encountered in the Jurassic Preuss salt. The salt section has historically caused many delays, millions of dollars of expenditures, and sacrifices in production casing goals. Fig. 1 depicts the current drilling and casing scheme in Anschutz Ranch East. To complete the wells with dual injection string or producer/injection string capabilities, 7-in. [17.8-cm] casing is required across the producing Nugget interval. To achieve this goal, a 17 1/2-in. [44.5-cm] hole is drilled through Tertiary and Upper Cretaceous sediments to a depth of approximately 5,000 ft [1524 m], where 13 3/8-in. [34-cm] casing is set. The intermediate 12 1/4-in. [31.1 -cm] hole is drilled through Cretaceous and Jurassic sediments and the salt interval, and casing is set in the top of the Jurassic Twin Creek formation. The final portion of the well is drilled with 8 1/2-in. [21.6-cm] bits through the Twin Creek and Nugget intervals, where a long string of 7-in. [17.8-cm] production casing is set. production casing is set. Successful drilling and casing of the salt interval is the key to the success of the entire drilling and casing program. Instances of stuck drillstrings, stuck casing, and program. Instances of stuck drillstrings, stuck casing, and collapsed casing prompted a comprehensive engineering study to determine the optimum salt-drilling and casing program and to explain the variances in the salt-drilling program and to explain the variances in the salt-drilling problem severity within the Anschutz Ranch East field. problem severity within the Anschutz Ranch East field. The study included postanalysis of all salt-drilling data from previous wells drilled along with logs and core evaluation. The study resulted in identification of the problem areas within the salt section and development of a problem areas within the salt section and development of a drilling program to handle these problem intervals.
Salt Section Characteristics
The Jurassic Preuss salt is encountered in the Anschutz Ranch East field at depths between 9,956 and 11,770 ft [3034 and 3587 m] on West Lobe wells and 12,354 and 12,750 ft [3765 and 3886 m] for East Lobe wells. The thickness of the salt interval varies from 35 to 1,232 ft [11 to 376 m] on the West Lobe and 55 to 412 ft [17 to 126 m] on the East Lobe. Generally, the salt interval is thin on the top of the structure and thickens down the flanks of the field (Fig. 2). Logs available for evaluation through the salt interval consisted primarily of cased-hole gamma ray (GR) cement bond logs (CBL's); however, a few openhole logs were examined. The character of the GR through the thick salt sections is typified by generally clean (low-API) GR with "dirty" intervals (slightly higher API GR). The dirty intervals are believed to be composed of siltstone and salt, with the siltstone content probably fairly high. By use of a method of graphic analysis whereby all drilling parameters and reaming and tight-hole intervals were plotted parameters and reaming and tight-hole intervals were plotted opposite rate of penetration (ROP) and GR log, the problem intervals (tight hole, reaming, etc.) were correlated problem intervals (tight hole, reaming, etc.) were correlated to the dirty intervals within the salt section. The dirty intervals varied in number and thickness depending primarily on the overall salt-section thickness. primarily on the overall salt-section thickness. Fig. 3 shows two four-arm caliper logs run over a typical 400-ft [122-m] salt section. The second log (Pass 2) was run after 14 hours elapsed with no operations of any kind in the wellbore.
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