After reaching target depth (TD) with Pressurized Mud Cap Drilling (PMCD) technique, risks associated with total lost circulation (including potential gas migration and unsustainable fluid logistics) have led to the perception that wireline logging and coring operations in PMCD are not feasible. However, with proper planning and procedures in place these operations are possible. Recent carbonate drilling operations in offshore Sarawak, Malaysia, have proven coring and wireline logging operations can be completed in PMCD conditions. In the first well, Well S, the operator retrieved core samples from three different zones in a gas bearing carbonate reservoir. The coring operation with PMCD, which was the first of its kind in the Asia Pacific Region, created new frontier for carbonate formation evaluation by allowing the acquisition of rock property data from wells once considered to be impossible to drill to TD. In another well, Well X, PMCD wireline logging operations were conducted safely and successfully. Open hole of 509 m was drilled with PMCD, and upon reaching TD the wireline logging pressure control equipment was rigged up to commence the PMCD wireline logging operation. In addition to the comprehensive planning and execution procedures, the increased riser pressure limitation was a main enabler for the PMCD wireline logging operations. Eight wireline runs were performed, collecting critical data for the field development plan (FDP). The gas water contact for the field was determined accurately despite the total lost circulation. Running wireline logging and coring operations with PMCD allowed the operator to not only drill once perceived impossible-to-drill wells, but also to retrieve crucial and valuable data from the well at TD. These operations reduce field volumetric uncertainty. This paper records the planning, execution, and post well analysis of carbonate sections, including the general methodology for the logging and coring operations in PMCD mode, risk and hazard assessment of the operations, results and observations of successful operations in Malaysia with elaboration of issues encountered, and recommended solutions.
Ultrahigh-pressure/high temperature (UHP/HT) wells are very challenging because of the narrow drilling margins, which can cause either losses or an influx. In a field in Malaysia, the pore pressure and fracture gradient were too close to allow conventional drilling, so the managed pressure drilling (MPD) technique was used to drill these wells.Cementing under MPD is a new technique in this area. A technical assessment revealed that there is limitation in the currently used cementing placement simulator in that it cannot simulate the real-time MPD cementing placement. The current hydraulic simulator does not account for automated real-time annulus choking to apply the backpressure and safely place the cement in the annulus. In addition, it does not take into account the downhole viscosity change due to pressure and temperature effects and which is not imposed by the testing protocols from API. To check the effect of the downhole conditions on the fluid viscosities, which will have an effect on the friction pressure in the annulus during the placement, and to reduce the risk during the cementing job, two in-house hydraulic simulators were identified and used to benchmark the currently used simulator results; the design workflow was changed to account for the additional simulations, and the new technique was implemented successfully to cement under MPD conditions.
The field subject of this paper is located in the southern Mexico, 34 km North of Villahermosa, Tabasco. Oil exploitation targets the Cretaceous and Jurassic formations (4500 mts a 5200 mts TVD). The 12 ¼" section of these wells must be drilled through a high pressure tertiary salt diapir which historically has been a high NPT generator due to high pressure salt water kicks and OBM contamination. Drilling strategy is usually oriented to the use of high density inverse emulsion mud with densities normally ranging between 1.95 to 2.27 SG (16.2 to 18.9 ppg). High density mud causes losses in the interfaces above and below the salt diapir and in some cases losses while drilling the salt diapir due to sand intercalations. A close analysis of the offset wells identified the MPD as a possible solution to mitigate the risks confronted in the section. This document describes the first application of the automated choke MPD system in Mexico, in a Sen well, and how the use of automated choke MPD system allowed drilling the section with no major operational events such as influxes, losses, stuck pipe or salt water contamination of OBM. The system helped detecting micro influxes giving tangible added value to this challenging narrow mud window hole section. As a result 938 meters of salt were drilled in only 11 days while field average is around 30 days. Introduction The field named "Sen" is surrounded by several other producing fields, Escarbado, Melocotón, Cardo (north boundary), Menta (west), Catarroso, Escuintle and Ricino (east) and Musgo (south boundary) (Fig. 3.2.1). Such field was discovered in 1984 with exploration well Sen 1 and its production began later in 1987 when the infrastructure was installed. The field has a drainage area of 29 km2, and an average thickness of 685 m with 229 m average net thickness. Productive formations are Upper, Medium and Lower Cretaceous, which are mainly comprised of mudstones, and the Jurassic which produces from dolomites. The hydrocarbon production comes mainly from the Upper Medium Cretaceous fractured reservoirs. The field is highly fractured and produces light crude of approximately 40° API. In terms of permeability and connectivity, it presents a high level of anisotropy. Production mechanism is water drive and the oil water contact (OWC) was determined at 5650 m.b.n.m.
Hydraulic modeling is a fundamental piece of any Managed Pressure Drilling operation using multiphase gasified drilling fluids. MPD Engineers rely on hydraulic flow modeling systems to predict equivalent circulating densities. Models also allow designing and manipulating hydraulic parameters such as gas/liquid ratios, pressures and flow rates to achieve desired conditions. Therefore, the selection and calibration of the correct hydraulic model is critical for the success of any MPD Operation. The ECD calculation in an MPD operation is not the solely objective of using a complex modeling system. Today's downhole drilling tools technology makes available a variety of sensors capable of measuring actual downhole pressure values. Prediction of flow behavior is also an important step that will increase the ability of monitoring and keeping efficient hole cleaning, cutting transport and heat transfer efficiency, which are critical for all multiphase drilling operations. Actual measurement of downhole equivalent circulating density becomes now a critical new calibration value to compare hydraulic models performance and approximation to reality. This paper compares the two-phase hydraulic simulations results with the data gathered from a drillstring installed annular pressure sensor used while drilling a highly deviated well in a low pressure reservoir using nitrogen injection through concentric string technique in an MPD operation. This technique poses a series of new challenges for the MPD engineer that needs to predict hydraulic behavior created by the typical transient "U" tube effect caused by connections, trips and surveys in this kind of applications.The paper details the model and calibration process, findings and best practices gathered from multiple runs, real time transmission and high definition memory data. Actual results and conclusions and also discussed and analyzed in depth for the benefit of any further concentric job applications associated with use of downhole pressure sensors.
The oilfields in study are important assets for the National Oil Company and represent 14% of the total oil production of the country. Two wide different and drastically challenging scenarios can be found: HPHT wells with a narrow mud weight window; and highly depleted wells in fractured carbonates. In both cases, the cementing job in production casings is historically classified as very difficult as a direct consequence of high frictional pressure losses due to the small annulus and deep wells configuration which causes loss circulation problems. A close analysis of the offset wells identified the use of MPD as a possible partial solution to mitigate the usual loss circulation scenario.This document describes the successful implementation of the MPD technique as a supplemental aid for cementing jobs, eliminating cement losses, avoiding formation damage, reducing mud losses by also offering additional safety to this kind of operations. In the last two years MPD has been used in a number of cementing jobs in HPHT wells and also in low pressure wells; with equivalent circulating densities as high as 1.65 sg. in both single phase and multiphase drilling fluids MPD applications as low as 0.29 specific gravity.Paper will also detail recommended operational procedures and recommended practices to integrate the MPD technique along with conventional cementing operations. The annulus between the 5" liner and the 7" liner 38# is very small, this condition associated with a narrow mud weight window, makes quite impossible to do a successful cementing job without the aid of the MPD technique.
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