Dual Openhole Gravel Pack in Shaly Fine Sands
- Giuseppe Moricca (Agip SpA) | Giuseppe Ripa (Agip SpA) | Domenico Rucci (Agip SpA) | Enzo Pitoni (Agip SpA)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- December 1995
- Document Type
- Journal Paper
- 226 - 232
- 1995. Society of Petroleum Engineers
- 2.4.5 Gravel pack design & evaluation, 1.8 Formation Damage, 2.2.3 Fluid Loss Control, 1.2.3 Rock properties, 5.6.1 Open hole/cased hole log analysis, 3 Production and Well Operations, 2 Well Completion, 1.1.6 Hole Openers & Under-reamers, 2.4.3 Sand/Solids Control, 3.2.5 Produced Sand / Solids Management and Control, 2.2.2 Perforating, 5.6.9 Production Forecasting, 1.14 Casing and Cementing, 4.1.5 Processing Equipment, 1.6 Drilling Operations, 5.5.11 Formation Testing (e.g., Wireline, LWD), 2.7.1 Completion Fluids
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This paper discusses the design and execution of dual-zone gravel packs invery shaly and silty formations of median sand grain size less than 30 um. Anoversized gravel was selected for sand control and, as consequence, theopenhole gravel-pack technique was adopted to reduce the effect of intermixingbetween formation and gravel-pack sand. During the completions in the firstfive wells, we encountered and solved several operational problems, includingthose involving (1) borehole stability, (2) setting of inflatable packer forzone isolation, (3) hole preparation, and (4) gravel placement. From thelessons we learned, another 11 wells were completed with dual openhole gravelpacks without significant problems. After 1 year of production, the flowperformance from the wells met or exceeded the initial objectives.
The Giovanna field is a gas-bearing reservoir situated in the offshoreAdriatic area (Fig. 1). It is a multiplayer reservoir comprising 30producing intervals that consist of thin interbedded layers of partiallyunconsolidated sand and shale. The total pay zone has a thickness of more than700 m and is located at depths between 1200 and 2000 m.
As a result of the small grain size of the sand and the high clay content,the reservoir rock has a very low effective gas permeability (10 to 30 md). Todevelop this reservoir, it was necessary to make provisions for a completionthat would prevent the movement of the incompetent sands. Because of the lowformation permeability, sand consolidation was immediately rejected as asuitable technique for providing sand control and consideration was given tomechanical methods (gravel packing).
In many cases, the inside-casing gravel pack (ICGP) introduces a largepressure drop across the completion,1 with a consequent reduction inthe production capacity and performance of the well. This result is especiallytrue when, as in this case, a very small size of gravel (100 to 120 U.S. mesh)is required. On the other hand, the openhole gravel pack (OHGP) generally isnot recommended in the presence of clays because there is a high probability ofintermixing with gravel. After careful analysis of the advantages anddisadvantages of each of these techniques, we decided provisionally to completeall 16 wells with OHGP's in dual parallel completion.
With only 16 wells available to develop the reservoir, it was necessary tocombine the 30 producing intervals into 11 producing pools. This decision wasbased on homogeneous pore pressure and depletion of the commingled producingintervals. As a result, it was necessary to complete long intervals (40 to 60m) for the exploitation of the gas resources. Because no previous experiencehas been gained with gravel-pack completions in very fine and silty sand, wedecided to proceed with the following course of action.
1. Perform a sand-flow test (SFT) to verify that sand production wouldoccur.
2. Execute a dual OHGP in the first well to ascertain the feasibility andefficiency of this type of completion.
Furthermore, a single ICGP was executed at a later stage and confirmed thatthe OHGP was the most appropriate completion for the Giovanna field.
This paper will illustrate the problems encountered, the remediesintroduced, and the results obtained from these completions, with particularreference to (1) evaluation of the risk of sand production, (2) gravel-sizeselection, (3) borehole stability, (4) zone isolation, (5) hole preparation,(6) gravel placement, and (7) flow efficiency.
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