Operator Drills Offshore in Unstable Formation and HPHT Environment

Overview

The operator planned to drill an offshore exploratory gas well in the Red Sea, targeting a stratigraphic trap in an unstable carbonate, sandstone, and siltstone formation with expected high bottomhole temperature (BHT). Such conditions would require the use of a superior fluid system, allowing the operator to efficiently drill the reservoir without incurring wellbore stability problems or thermal degradation of the chemical package. In drilling to a total vertical depth of 19,050 ft MD in this environment, the main concerns were with regards to fluid stability during logging operations, fluid loss, chemical treatment plans and avoiding conditioning trips or extra circulation that would lead to non-productive time (NPT). 

Challenge

Given the uncertainties they faced, the operator had to be prepared for potential washouts and mitigating issues of equivalent circulating density (ECD), tight spots, stick and slip, torque and drag, barite sag, overtreatment, and conditioning time. Halliburton Baroid was commissioned to deliver a single solution capable of overcoming these multiple challenges. The client authorized the design of a customized fluid system along with extensive lab testing to withstand BHT as high as 416° F, while reducing the thermal degradation of the chemical package, and with all the characteristics needed to execute the drilling and logging phases with no downhole problems or excessive NPT. 

Solution

The INNOVERT fluid system with a high-temperature fluid loss reducer and an improved suspension package was validated prior to drilling the section. The unique chemistry of this HPHT fluid system allowed the operator to reach TD without thermal degradation. It was specially designed for superior solids suspension and extremely tight fluid loss, even in high temperatures, which minimized barite sag and prevented differential stuck pipe events while drilling or logging. The chemical package, consisting of the BaraFLC®-IE 513 fluid loss control agent and TAU-MOD® viscosifier further guaranteed tight fluid loss and proper emulsion, respectively.  

Result

The INNOVERT fluid system and high-temperature chemical package was the right solution, as it enabled vertical drilling of the well to a total depth of 19,050 ft MD without any downhole problems or NPT. The capability of the fluid system to overcome all the well challenges was translated into a saving of three days and USD 450k. Some specific accomplishments of this project were:

• The clay-free, non-aqueous fluid (NAF) delivered low ECD, which led to improving the drilling parameters and reaching the reservoir safely in less time. 
• The improved suspension package delivered superior sag prevention over an extended period of time, which allowed the operator to perform the logging phase without additional conditioning trips. 
• The chemical package, compared to conventional NAFs, reduced fluid treatment amount and, consequently, lowered cost.