Mud Erodibility Technology Impact on Cementing Operations1 Large Scale Experiments Have Shown Gelation plus dehydration of the mud across permeability is one of the main causes of mud displacement (removal) problems Beirute Consulting, L.L.C. 2 Large Scale Experiments Have Shown (cont.) • Extended shutdowns: very detrimental to the hole cleaning (circulatable hole) process • Age: of the Partially Dehydrated-Gelled (PDG) mud: very detrimental • Removal of the PDG: Requires energy Beirute Consulting, L.L.C. 3 Vertical Hole - Large Scale Experiments PDG Formation Cement Casing Beirute Consulting, L.L.C. 4 C. L.Large Scale Experiments PDG and settled solids Beirute Consulting.Inclined Hole . 5 .L. L. L. 6 .Beirute Consulting.C. L.Next Step Study mechanism of mud cake deposition and erosion with the goal of developing better means for improved removal Beirute Consulting. 7 .C. L. L. L. 8 .Objectives • Build an experimental setup to study the mechanism of mud deposition and removal • Develop a mathematical model • Recommend procedures for field operations Beirute Consulting.C. L. 9 .Model about 20+ ft long Beirute Consulting.L.C. L. 100 psi differential Beirute Consulting. L. 18 hrs. 1hr – Filtrate collected Mud circulation: 3 and 5 BPM – Filtrate collected Shutdown.Experimental Procedure • Day 1: – – – – – Water calibration in turbulent flow Mud calibration: 2. 10 .C. 4 BPM .No filtrate collected Mud circulation: 1 BPM. ) • Days 2 and 3: – Mud circulation at 1 BPM to near steady-state – Same as above at 2. 11 .L.Experimental Procedure (cont.C. 3 and 5 BPM – Shutdown with 100 psi differential Beirute Consulting. L. L.Experimental Procedure (cont. 12 .C. L.) • Day 4: – – – – Same as day 2 Spacer fluid pumped Cement slurry pumped Model cured for 48 hrs • Later: – Model cut in sections – Observations made – Pictures taken Beirute Consulting. Example Beirute Consulting. 13 .L.Tests Results .C. L. L.Beirute Consulting.L.C. 14 . L. 15 .Beirute Consulting.L.C. L. 16 .L.C.Beirute Consulting. C. 17 .Beirute Consulting. L.L. L.C. 18 . L.Beirute Consulting. Beirute Consulting. 19 .C. L.L. L.C. L. 20 .Beirute Consulting. L. 21 .Beirute Consulting.C.L. 22 .C.L.Beirute Consulting. L. L.Beirute Consulting.C. 23 . L. 37 0.L.PDG Thickness vs.338 0. 24 .C.44 ~2 0.375 Day5 0.40 ~3 0.41 0.402 Beirute Consulting.415 0.4 0.373 ~5 0. Time PDG Thickness (in) Rate (bpm) Day 2 Day3 ~1 0.335 0. L. the harder it is to remove it Beirute Consulting.Important Conclusions • Rate (wall shear stress) is needed to remove the PDG • Extremely high rates can be detrimental to the PDG removal process • The older the PDG. L. 25 .L.C. Proposed Mechanism • Opposing Forces: – Differential pressure against permeability causes the deposition of filter cake and PDG – Erosion by flowing fluid tends to remove the PDG • PDG drilling fluid and filter cake are eroded as long as pressure drop (wall stress) in the annulus exceeds a certain value • Shear stress at the wall: hydrodynamic force responsible for the erosion • Adhesion forces: resistance to erosion Beirute Consulting. L.L.C. 26 . L.) • Erosion takes Place for as long as the shear stress at the wall (point of contact between the flowing fluid and the static PDG or filter cake) exceeds the yield stress of the PDG or filter cake.C.Proposed Mechanism (cont. Beirute Consulting. L. 27 . 28 .L.Compare magnitude of the values Can the stress of the PDG be inferred from normally reported mud properties? Beirute Consulting.C. L. L.C. 29 .Conversion Factor • Wall Shear Stress and Friction Pressure relationship: τ = De x ∆P/4L Wall Stress (lb/100 ft2) = 300 x De (in) x ΔP (psi)/(4 x L (ft)) ΔP (psi) = Wall Stress (lb/100 ft2) x L (ft)/ (300 x De (in)) Beirute Consulting.L. L.C.Beirute Consulting. L. 30 . Beirute Consulting. L. 31 .C.L. Beirute Consulting.L. 32 .C. L. 33 . L.C.L.Beirute Consulting. C. 34 . L.Beirute Consulting.L. L.L. 35 .Beirute Consulting.C. C.L. L. 36 . Then: • Develop and test erodibility cell • Test erodibility of muds • Design rates and spacer properties to erode PDG and filter cake Beirute Consulting.Lab Work • Since stress levels of the PDG need to be measured in the lab to be able to design jobs to effectively erode the PDG. L.C.Large Scale Test Cell Beirute Consulting. L. 37 . MOBM and SOBM have been found to be thinner and easier to remove that those generated by water base muds.PDG’s of Different Muds • Over all. etc.L.C. Levels: ~ 25 lb/100ft2 • Worst PDG’s are those generated by poor quality water base mud’s: poor fluid loss control. PDG’s of oil base. 38 . progressive gels. L. Levels: as high as 100 + lb/100ft2 Beirute Consulting. Using a Simulator and lab Measurements to Better Design Cement Jobs 39 . Beirute Consulting.L. 40 . L.C. L.C. 41 . L.Beirute Consulting.