A Novel Approach Towards Cementing Design Achieved Significant Improvement in Long Term Zonal Isolation

Abstract

Well integrity is becoming more challenging with drilling of deeper, highly deviated and horizontal wells worldwide while the current market scenario is driving every stakeholder to execute their scope of work under ever revising AFEs. The scope of this paper is to present an optimized approach to improve quality of cement jobs while having a good long term zonal isolation across all the targeted formations and further eliminating the additional costs required for remedial jobs. There are various challenges that need to be dealt with when cementing complex wells such as uneven cement distribution around the casing due to insufficient mud removal, inadequate hole cleaning and poor casing standoff. All these challenges were addressed by in-house developed optimization methodology. The elements of this methodology that positively influenced the quality of the cement bond were (i) Optimizing the rheological hierarchy between the cement, mud and spacer design to create optimum flow during the cement job (ii) Improving hole cleaning efficiency by applying tailor-made spacer technology with aid of modeling software (iii) Optimizing the centralizer profile by including non-survey stations. The in-house developed optimized methodology has yielded excellent results with significant improvement in the cement bond logs when compared to the offset wells. This paper will present the methodology adopted in detail along with the field example of a well in an offshore island that has measured success against the key improved elements. The rheology of the fluids was adjusted to improve the fluid displacement in the analytical software which has played a big role in improving the hole cleaning efficiency. In addition, application of tailored Spacer design has not only showed improved mud removal effectiveness but also helped with reducing the channeling alongside the best optimized centralization found in the field in terms of type, quantity and placement across various formations and direction profiles along the well bore. This paper will also compare different logs in the same field to show the improvement against the new methodology and practices adopted that helped in achieving complete zonal isolation across all formations. The new optimization methodology has resulted in significant improvement in outcome of cement logs across production casing in offshore island indicating an excellent zonal isolation and adherence to well integrity requirements. The key elements that were improved are now being adopted across all the jobs in the field and nearby fields.