Primary Cementing by Reverse Circulation Solves Critical Problem in the North Hassi-Messaoud Field, Algeria
- R. Marquairi (Compagnie Francaise Des Petroles (Algerie)) | J. Brisac (Compagnie Francaise Des Petroles (Algerie))
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- February 1966
- Document Type
- Journal Paper
- 146 - 150
- 1966. Society of Petroleum Engineers
- 1.14 Casing and Cementing, 4.2.3 Materials and Corrosion, 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 1.6.9 Coring, Fishing, 5.2 Reservoir Fluid Dynamics, 4.1.2 Separation and Treating, 1.6 Drilling Operations, 1.14.3 Cement Formulation (Chemistry, Properties), 4.1.5 Processing Equipment, 3 Production and Well Operations
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After usual cementing techniques failed to give satisfactory results, a systematic analysis of difficulties resulting from high pressures and weak down-hole formations led to the development of a reverse cementing technique. This method has now been used successfully for the past two years on all development wells drilled in the North Hassi- Messaoud field in Algeria. Its application required a modification of the regular differential fill-up equipment and wellhead assembly. The particular drilling and cementing problems encountered in this field are described in detail along with the technique and equipment used to solve them.
A regular drilling schedule for a North Hassi-Messaoud well can be divided into four main steps (Fig. 1): 1. A 17 3/8-in. hole is drilled from 0 to 750 ft using a 10 lb/gal bentonite mud improved with CMC (sodium carboxymethyl cellulose). A 13 3/8-in. casing is set and cemented up to the surface. 2. A 12 1/4-in. hole is drilled from 750 to 1,800 ft using the same mud. At this depth the mud is converted to a salt-saturated type with a density increasing from 11 to 12 lb/gal. The hole is drilled to 7,500 ft, where an intermediate 95/8-in. casing is set. 3. An 8 3/4-in. hole is drilled to 11,000 ft using the same salt-saturated mud weighted with barite up to 18 lb/gal. A 7-in. production casing is set on the top of the pay zone, the Cambrian sandstones. 4. The reservoir is cored with 5 15/16-in. diamond core heads using a 12- to 13-lb/gal oil or water base mud.
Why Conventional Cementing Techniques Fail
Difficulties in Drilling the 8 3/4-in. Hole
Three major difficulties are encountered during the drilling of the 8 3/4-in. hole.
High-Pressure CaCl2 Formation Water
At 8,500 ft in the lower Jurassic, a high pressure, 8,500 psi, CaCl2 -saturated water producing formation is encountered. This formation consists of thin beds of porous and locally vesicular dolomite. The water contains 370 ppm of free HCO3 and 430,000 ppm of CaCl2. Mud contamination by this fluid is spectacular. To prevent this water from coming into the hole during drilling, a mud weight of 17 to 18.5 lb/gal is required. The exact amount depends on variations in permeability and the existence of fine fissures in the formation. However, when making trips, some of this water comes into the hole. It varies from 6 to 90 bbl and badly contaminates large amounts of mud which have to be circulated out and separately reconditioned.
Located between two massive Triassic salt beds, a clay zone about 15-ft thick is encountered at 9,500 ft. These clays are sufficiently plastic so that they continuously extrude into the wellbore. The only remedy is the use of adequate mud weight (17 to 18.5 lb/gal) to balance the formation. Other methods to control these clays (use of shale control type or extreme low filtration water base muds) have failed.
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