Wellbore Stabilization Increases Fracture Gradients and Controls Losses/Flows During Drilling

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper presents formation treatment technology that helps (1) reduce well-construction costs, (2) improve and maintain wellbore integrity during drilling, and (3) enable economical production from reservoirs with challenging drilling and cementing conditions. The technology presented helps stabilize and improve wellbore conditions by several different downhole mechanisms and types of sealing materials. This paper emphasizes one of the most promising of these mechanisms: increased near-wellbore fracture gradients (NWFG), or wellbore pressure containment (WPC) caused by stress alterations in the rock surrounding cracks induced by sealants forced into the cracks to slightly widen them near the wellbore. Industry studies 1,2 sometimes refer to these stress alterations as "stress cages." The alteration process 3 has been described as a WPC failure mechanism in which tensile force switches to compressive force as the fracture is sealed near the wellbore. Each side of the wellbore connecting the two fracture wings is moved by the compressive force in directions perpendicular to the fracture plane and proportionally to the increase in fracture width. As a result of this WPC improvement, engineers may plan wells with fewer casing/liner strings and with upper hole sections of smaller diameter. Under certain conditions, it is possible to construct the "one-trip" well, wherein only one bit-run is needed to drill to total depth (TD) from the surface-casing shoe. The new technology can also help prevent or mitigate unstable hole conditions that interfere with the drilling process.Wellbore-stabilization technologies presented are designed for wells with narrow mud-weight windows (MWW) that can lead to well-construction incidents such as (1) loss of circulation, (2) failed shoe tests, (3) poor annular zonal isolation, (4) the need for extra strings of casing to enable drilling through depleted formations, and (5) lack of sufficient mud weight to prevent hole collapse and gas kicks. The key process in the system is placement of sealant in wellbore cracks to strengthen the wellbore to enable the use of a greater range of mud weights, i.e., a wider MWW.Results from a numerical simulation analysis model are reported. The model is an aid to well planners in their efforts to design wells with (1) fewer casing strings, and (2) smalldiameter upper-hole casings.Case histories from around the world indicate that this process can result in substantial cost savings and that it represents a real breakthrough in drilling and completion technology. Improved primary cementing and sustained annular zonal isolation during production are also described. The fracture gradient (FG)-increasing treatments were applied during drilling to prevent lost circulation while cement slurry was being placed in setting casing and liner strings. Production cost savings included shorter periods to start of production, improved well integrity, prevention of annular wellhead pressures, no skin damage in reservo...

The Evaluation and Application of SmartGel for Deepwater Loss-Circulation Control

“…1.24 g/cm 3 . Formation pore pressure: 1.20 g/cm 3 . Temperature: 60 • C. Formula of drilling fluid: 0.2% NaCO 3 (sodium carbonate) + 0.17% citric acid + 3% PF-1 (polyamine, Shale inhibitor) + 0.8% PF-2 (coating agent) + 3% PF-3 (coating lubricant) + 2% PF-4 (fluid loss reducer) +2% PF-5 (borehole stabilizer) + 9% NaCl (potassium chloride) + 0.1% NaOH (sodium hydroxide).…”

“…Lithology: Grey mudstone, grey silty mudstone and argillaceous siltstone. Depth of casing shoe: 2865.38 m. F.I.T @casing shoe: 1.65 g/cm 3 . Density of drilling fluid: 1.21 g/cm 3 .…”

“…Depth of casing shoe: 2865.38 m. F.I.T @casing shoe: 1.65 g/cm 3 . Density of drilling fluid: 1.21 g/cm 3 . Drilling ECD: Max.…”

“…Judging from the return of mud logging cuttings, the lithology of 3012~3018 m is muddy siltstone, and the bearing capacity of the formation is low. During the drilling of this well section, the density of drilling fluid was 1.21 g/cm 3 , and then it was gradually increased to 1.25 g/cm 3 , which was measured from the shale shaker. The target formation was uncovered and drilled to the coring formation, and there was no loss-circulation.…”

“…The lithology of the second member of the Yinggehai Formation in the Lingshui block is mainly gray mudstone, argillaceous siltstone, and gray silty mudstone. Generally, the interface between mudstone and sandstone is prone to produce stress "weak points" of tectonic movement, and there are interface fracture zones between mudstone and sandstone, thus forming more loss-circulation formation [1][2][3]. In addition, because the formation fractures in the second member of the Yinggehai formation mostly appear in the form of transverse fractures, and Processes 2023, 11, 1890 2 of 12 sandstone has good permeability, once subjected to hydrostatic pressure, the fractures will be easily pushed open and spread around quickly, resulting in continuous loss-circulation, which greatly increases the difficulty of plugging in drilling [4][5][6].…”