Bridging Agents Optimization Based on Predicting Induced Fracture Model for Deviated Wells – A Case Study

Applying bridging agents to prevent seepage losses is a common practice during drilling reservoir sections which limits the invaded zone and reduces stuck pipe possibility. Unfortunately, the initial particle size distribution (PSD) design of bridging agents based on static models does not prevent actual seepage losses due to the induced fractures which have different sizes comparing to the initial reservoir pore sizes. This paper reviews an actual case study with provided solutions in an offshore field located in the Middle East which had a seepage loss circulation problem through induced fractures. It also presents analyzing natural and induced fractures size of the reservoir layer to choose optimized possible bridging agents’ PSD to cure/prevent loss circulation problems. The maximum/average pore size of formation can be measured from routine core analyses. A geological method to estimate the induced fracture widths with geo-mechanical data were used. Finally, optimum blends of bridging agents for loss circulation pills or background treatment to prevent mentioned problems were designed. Based on the laboratory testing on cores taken from previously-drilled wells in the mentioned field, the maximum size of pore throats was measured as 20 microns. Therefore, using the Ideal Packing Theory (IPT) method, the result for selecting bridging agents through pore throats (for seepage loss) indicates that optimum treatment is using of bridging agents with D50 and D90 6.5 and 16 microns, respectively. Also, for improving the treatment selection through parameters such as PSD of bridging agents, investigation on behavior of fracture growth were done. As a result, induced fracture width in studied well, with provided geo-mechanical (such as Poisson's Ratio & Young Modulus) and drilling fluid data was calculated approximately to be 230 microns through the porous medium in the near-wellbore region. Therefore, optimization for bridging these new fractures while drilling was performed again and it was concluded that optimum bridging agent size distribution at the tip of these newly-created induced fractures is applying bridging agents with D50 and D90 of 64 and 170 microns respectively, which are approximately 10 times higher than normal treatment in size. This paper describes the historical seepage circulation and related problems in the mentioned field and presents a methodology to prevent these issues by predicting induced fractures and optimizing bridging agent PSD to block them. Considering this methodology, the gap between the design and actual drilling is reduced and both rig downtime and related drilling and drilling fluids costs can be saved.

A study on water seepage losses for ponds and reservoirs

Irrigation is main factor for agricultural production. Our aim is to increase agricultural yield by increasing area under irrigation. It is very important to see that more water available for irrigation is completely used as far as possible to avoid water loss during conveyance through canal. Seepage loss is major water loss during transit. Rainwater harvesting is the artificial collection, storage and use of runoff or rain water. The water harvesting with tanks and ponds is one option to increase water availability and agricultural production at the household level. Rain fed agriculture can be protected by adopting farm ponds. The harvested runoff water in a farm pond creates salinization / water logging problems so; it has to be lined to control the seepage losses. The article presents a review on the type of lining materials viable and to explore for a cost effective sealant which can be adapted. In comparison to clay lining, Bentonite, polymers like HDPE, LDPE, Silpoulin, LLDPE in combination with concrete increases the durability along with the 100% seepage control with benefit cost ratio for HDPE lining in combination with concrete showed highest value of 10.4:1. Bentonite, though costly has shown significant results by reducing the seepage losses by 72% to 96% respectively, depending on the thickness of application. In vertisols, lining did not show any significant variation. Whereas alfisols, luvisols of arid and semi-arid regions require lining materials with diversified crops and conservative irrigation practices.