Deepwater drilling presents significant issues and uncertainties, especially when there is no prior drilling experience in country or only limited offset information is available. Uncertainties about the drilling conditions create additional risk to operators and can cause project budget increases. Therefore, innovative technologies are often implemented to help ensure that the well is drilled efficiently and safely, operators obtain well data and important geological data that can help identify potential reservoirs and wells in the area. Petrobras Colombia undertook the challenge of drilling the first deepwater well in Tayrona BLock located in the Colombian Caribbean, in approximately 1,840 ft water depth. Drilling fluid selection was a key decision to the success of the project due to the nature of the exploratory project, formation uncertainty, environmental footprint, wellbore stability and protecting any potential reservoirs. A high-performance water-based fluid (HPWBF) was selected to drill the well based on the following criteria;The ability to discharge to the sea without environmental impactEffective inhibition capability to drill reactive clay formationsNon-dispersed, low-solids formulation to improve rate of penetration (ROP)Shear-thinning behavior for excellent hole cleaningHigh and low temperature as well as high-pressure stabilityLubricity, wellbore stability and low equivalent circulating density (ECD) values. The HPWBF provided excellent performance as demonstrated by trouble-free trips, casing, cementing and wireline logging operations. Rheological properties remained stable during changes in temperature and pressure, confirming reliable fluid stability and reducing costs associated with non productive time (NPT). Although the inhibition provided by the fluid system was excellent, the wellbore exhibited some mechanical instability related to stress distribution. No bit balling problems were observed and ROP was acceptable most of the time. Wiper trips required less time than expected and did not present any issues. In conclusion, the HPWBF demonstrated excellent performance in all aspects and contributed to the overall project success in obtaining important formation data, minimizing NPT and reducing costs related to fluid and cuttings disposal. Introduction Deepwater exploration activity in the oil and gas industry continues to present new hurdles requiring innovative technical solutions. These difficult wells can increase the risk factor and result in potentially higher operational costs. In most cases an oil-base drilling fluid is selected as the first option in light of the high daily costs associated with a deepwater operation, and the advantages gained in wellbore stability and ROPs compared to conventional water-based systems. However, tightening environmental regulations and high costs associated with cuttings and oily fluid disposal is sufficient to seek viable water base fluid alternatives that could yet provide an oil base drilling fluid performance. For this reason, drilling fluid companies constantly investigate and design state-of-the-art water based drilling fluid systems that can provide performance similar to an oil-based fluid but can be discharged directly to the sea with a reduced environmental footprint.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper describes a new design procedure developed to help effectively remove drilling fluid components, particularly thick layers of partially dehydrated filter cake, from the casing/wellbore annulus after the fluid has been exposed to downhole conditions, including, temperature, pressure, fluid loss, and static time. This new methodology can be conducted in any properly equipped cementing and drilling fluids laboratory.To isolate the zones of a well and allow a reservoir to be produced safely and economically, drilling fluid and drill cuttings should be removed from the annulus and replaced by a competent cement sheath that bonds and seals the casing to the wellbore. Simple laboratory tests performed with commercially available testing devices help the designer evaluate the cleaning efficiency of flushes, spacers, and surfactants under simulated downhole conditions. These tests can determine the following parameters:• Force required to mobilize the drilling fluid • Chemical effects of preflushes and/or spacers used for mud removal and filter-cake removal and their effect on filter-cake permeability These parameters, combined with a mathematical model that helps determine the fluid properties and annular velocities required to effectively remove drilling fluid, provide a realistic simulation of the displacement process.Case histories and well logs illustrate how the displacement process can be significantly improved when designers use a procedure that includes the following steps:1. Conduct laboratory tests. 2. Run a mathematical simulation model. 3. Design fluids to address issues such as cementing across unconsolidated and/or high-permeability formations.
Hundreds of wells have been drilled since the early 1900's at the Putumayo basin in southwest Colombia. ECOPETROL (NOC) used traditional mud systems: lignosulphonates, potassium chloride, and finally lime or gypsum mud systems, all of them designed to manage exposure to anhydrite, a common mineral in the drilled formations. The calcium contamination adversely affects mud system properties, resulting in hole instability and frequent stuck pipe events. Because of these issues, the operator considered using oil base mud (OBM) in a very environmental sensitive area. The OBM would generate undesirable waste and there were uncertainties about its performance, since few wells in the area had been drilled with OBM and the results were not very successful. Therefore, for drilling operations on the ECOPETROL Sucumbíos No. 5 well, a completely new high performance water base mud (HPWBM) was proposed and accepted. The new chemistry eliminated the use of bentonite and included a new flocculation inhibition mechanism, as well as new and powerful polymers. The system demonstrated that calcium and anhydrite were not a problem any more and the well was drilled in record time. More importantly, to the operator was able to evaluate the productive formations by running electrical logs, an operation that was normally cancelled because of severe hole problems. Casings strings were set and cemented per the well program and the well was completed as planned. This paper presents the design state of the HPWBM, its performance while drilling and charts and graphics comparing the changes against the historical values recorded in the area.
The Lisama field located in the middle Magdalena basin is well known as one of the high pressure areas drilled in Colombia by ECOPETROL (NOC). Densities up to 21.0 ppg are often reached and side tracks due to hole instability are common in the area, sometimes as many as three (3) per well, making plans in days and costs difficult to control. The use of real time tools such as Pressure While Drilling (PWD) on the Lisama No 167 well demonstrated that only monitoring the fluid density at surface is not enough to keep the hole open and stable. Monitoring with PWD demonstrates that real annulus pressure involves all kind of parameters affecting the mud density including temperature, solids content and compressibility, so that the real pressure and the Equivalent Mud Weight (EMW) can be determined at any point of the wellbore. In this directional well, the challenge for the service company is to use an MWD system that works with high-density fluid conditions. Conventional systems have an operational limit of 18.0 ppg, so an electromagnetic telemetry system was chosen. Through continuous ECD monitoring and EMW management, combined with a good drilling plan plus the use of electromagnetic telemetry systems, it was possible to keep the wellbore under control and reduce operational time to 60% below the offset wells drilled in that area. The Lisama No. 167 well reaches expected densities around 21.0 ppg, enough to keep pore pressure under control and drill to the final depth of 7390 ft without problems. The successful combination of PWD tool plus electromagnetic telemetry made it possible to identify the events requiring improved hole cleaning, increased mud weight and optimized drilling parameters. It also facilitated decisions regarding circulating, tripping or casing point selection.
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