Open hole multilaterals
15 March 2018
Hello folks. We're discussing drilling two 6" lateral horizontal wellbores below a 7" liner. The plan under discussion is to drill the higher lateral first then the lower one, with an azimuth difference of something like 50 degrees between the laterals. The 7" shoe will be at around 55 deg inclination. After drilling the laterals, we'll need to run CT into each lateral for stimulation.
Question is, whether cuttings building up in the upper lateral would prevent getting in with CT to do the stimulation and what might we do to mitigate that?
In these wellbore sizes (6in) and as since a key objective would surely be to assure maximum productivity at minimum formation damage.
Using the right drill in fluid and assuring turbulent flow (that should be readily attainable in 6in wellbores) during operational activities should reduce cuttings build up risks to ALARP.
Use of a WARP based fluid technology or a similar drill-in fluids approach if capital efficiencies allow this, could enhance all such aspects.
Besides drilling the bottom lateral first? The first answer is helpful, use the same BHA and string to find it as use to make it, whether you've deposited cuttings in the hole or not. Perhaps looking at it as minimizing the cuttings finding the opening of the top lateral is the perspective to have. Cuttings in a vertical hole tend to seek the low pressure at the surface we know so there really isn't any pressure to pull or push cuttings into the top lateral per se except during connections. Gel Strength etc are factors worth considering yet also the angle of the top lateral at the KOP of the bottom lateral from the low side at an angle high enough then any cuttings beds will not avalanche into the top lateral. If that mitigation is too uncertain and/or costly then a retrievable liner might hangoff in the last casing string and cover then top later yet I don't know the footage nor if the risk of not retrieving it stuck in place and all the operational costs to hang/retrieve/etc is worth the risk/costs of 1) losing the top lateral. Spot a detectable marker fluid with super high viscosity inside the top lateral will accomplish perhaps an effective barrier to debris and also a market to find the top lateral latter on.
Hope that helps.
An experience from the multilateral project I have done, after the last leg drill, then all the previous leg drilled needed to re-enter again to make sure the hole was there and accessible. The way we use to do is using the same bha we use to drill it, but some time it's just does work to use the same bha, therefore we run so called a "hole finder" bha, which is just a slick pipe with big bend pipe on the lower end (a very simple bha, but works well to re-enter the drilled open hole).