One of the major problems in drilling industry that increases non-productive time, expenditures and environmental damages is Lost Circulation problem of drilling fluids. Lost Circulation in formations in low pressure or unconsolidated formations can be prevented with applying appropriate wellbore strengthening materials (WSM) which mitigate formation damages and provide with having a high production index after drilling operation. In this paper, designing of wellbore strengthening materials with different mechanisms are discussed and investigated.
Considering comprehensive study on different bridging mechanisms, resilient/deformable materials, organic fibers, and also investigation on optimizing particle size distribution of WSMs, two engineered solutions were designed and evaluated using Loss Circulation Material (LCM) Tester Equipment which has a cylinder structure, also pressure valve is set up on the upper cap and a tailor-made sand bed or slotted disk is fitted on its bottom. Different type of oil-based and water-based drilling fluids with and without designed WSMs were poured into the LCM Tester equipment, then 650-psi pressure was applied for 30 minutes. For each fluid, the invasion depth and invasion rate of the fluid into the sand bed was reported, also rheological properties and API Fluid loss were measured.
According to the results, invasion depth and invasion rate of fluids containing designed WSMs is magnificently lower in comparison with drilling fluids which not contained any WSMs. Drilling fluids contained the designed WSMs are highly-effective in both reservoir and non-reservoir formations for stabilizing the wellbore and preventing seepage loss in sandstones and mini-fractured formations. Evaluation of rheological properties and API-Fluid loss (before and after hot-rolling in 250° Fahrenheit for 2 hours) and comparing them with blank samples confirmed that designed WSMs did not have major adverse effect on rheological and fluid loss parameters. Designed WSMs in this paper can hold pressures as high as 650 psi in LCM tester equipment on (sand bed with permeability up to 5 Darcies) or slotted filter disks (up to 200-micron fracture width). Last but not least, regarding wellbore strengthening mechanisms, one of the WSMs includes dual bridging mechanisms in sandstone formations and the latter includes forming a stress cage in the wellbore surface that causes to decreasing permeability of the formations while drilling due to expansion of its designed resilient materials in the fractures.
Main goal of this research is using environmentally-friendly and economic waste materials to design highly effective WSMs. One of the designed WSMs includes environmentally-friendly organic waste fibers as a higher concentration additive. Additionally, one of the designed WSMs is more than 80% acid-soluble in 15% hydrochloric acid and the other one will be detached and left the wellbore pore-throats with beginning of production without any damage to reservoir zones.