A Practical Approach for Preventing Lost Circulation in Severely Depleted Unconsolidated Sandstone Reservoirs
- A. Ali (Amoco Trinidad Oil Co.) | C.L. Kalloo (Tucker Group of Companies) | U.B. Singh (Amoco Trinidad Oil Co.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- March 1994
- Document Type
- Journal Paper
- 32 - 38
- 1994. Society of Petroleum Engineers
- 1.10 Drilling Equipment, 1.14.4 Cement and Bond Evaluation, 1.14.3 Cement Formulation (Chemistry, Properties), 3 Production and Well Operations, 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 4.1.2 Separation and Treating, 1.14 Casing and Cementing, 1.1.6 Hole Openers & Under-reamers, 1.6.1 Drilling Operation Management, 2.4.5 Gravel pack design & evaluation, 1.8 Formation Damage, 2.4.3 Sand/Solids Control, 2.2.3 Fluid Loss Control, 2.2.2 Perforating, 1.11 Drilling Fluids and Materials, 5.6.1 Open hole/cased hole log analysis, 1.12.1 Measurement While Drilling, 4.3.1 Hydrates, 4.1.5 Processing Equipment, 1.6 Drilling Operations, 1.11.4 Solids Control, 4.2 Pipelines, Flowlines and Risers, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc)
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This paper discusses the field application of a blend of lost-circulation materials (LCM's), in a water-based drilling fluid to drill through multiple severely depleted, unconsolidated sandstone reservoirs. Simple laboratory tests are documented to show the sealing effectiveness of the LCM blend. Major benefits of the LCM blend include lost -circulation prevention, elimination of intermediate-drilling-casing strings, and substantially lower well costs.
Lost circulation is one of the oldest, most time consuming, and costly problems encountered in drilling a well. Off the east coast of Trinidad, the problem is no different. Lost circulation, or loss of returns, is defined as the loss of drilling fluids or cement slurries into the formation. Generally, four types of formations are responsible for lost circulation: (1) natural or induced formation fractures, (2) vugular or cavernous formations, (3) highly permeable formations, and (4) unconsolidated formations.
The industry has developed three types of agents to combat lost circulation: (1) bridging, (2) gelling, and (3) cementing agents; the type used depends on the operational phase of the well.All these types of agents have been used to combat lost-circulation problems in wells offshore the east coast of Trinidad. In this area, bridging agents are far more effective than cementing or gelling agents for handling lost-circulation problems. Bridging agents can be classified as fibrous, flake, granular, or blended.Although all these bridging agents have been used, the blended type seems to cure lost circulation best offshore Trinidad.
Most of the east coast producing fields contain multiple unconsolidated sandstone reservoirs with permeabilities from 50 to 100 md. These reservoirs, which have been partially or severely depleted because of hydrocarbon production, lie below virgin-pressured water-bearing sands and, in some instances, above virgin-pressured hydrocarbon-bearing reservoirs. Partial loss of mud circulation is almost certain to occur during drilling through these subnormally pressured sands; complete loss of mud returns is common when the sands are severely depleted. Consequently, several lost-circulation-related problems have developed that have led to higher well costs. For example, on several occasions when partial losses occurred, the drillstring became differentially stuck because of high differential pressure across the depleted sand. In other cases, the drill string became packed off and stuck because the open hole above the bit caved in. This occurred because of hydrostatic pressure loss when complete mud returns were lost.
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