Showing papers in "Spe Drilling & Completion in 2012"

Decreasing Water Invasion Into Atoka Shale Using Nonmodified Silica Nanoparticles

Abstract: This paper (SPE 146979) was accepted for presentation at the SPE Annual Technical Conference and Exhibition, Denver, 30 October–2 November 2011, and revised for publication. Original manuscript received for review 21 June 2011. Revised manuscript received for review 6 December 2011. Paper peer approved 21 December 2011. Summary Fluid penetration from water-based muds into shale formations results in swelling and subsequent wellbore instability. Particles in conventional drilling fluids are too large to seal the nano-sized pore throats of shales and to build an effective mudcake on the shale surface and reduce fluid invasion. This paper presents laboratory data showing the positive effect of adding commercially available, inexpensive, nonmodified silica nanoparticles (NP) (particle sizes vary from 5 to 22 nm) to water-based drilling muds and their effect on water invasion into shale. Six brands of commercial and nonmodified nanoparticles were tested and screened by running a three-step pressure penetration (PP) test (brine, base mud, nanoparticle mud). Two types of common water-based muds, a bentonite mud and a low-solids mud (LSM), in contact with Atoka shale were studied with and without the addition of 10 wt% nanoparticles. We found that a large reduction in shale permeability was observed when using the muds to which the nonmodified nanoparticles had been added. For the bentonite muds, the permeability of Atoka shale decreased by 57.72 to 99.33%, and, for the LSMs, the permeability of Atoka shale decreased by 45.67 to 87.63%. Higher plastic viscosity (PV) and lower yield point (YP) and fluid loss (FL) of the nanoparticle muds compared with base muds were also observed. We also found that nanoparticles varying in size from 7 to 15 nm and a concentration of 10 wt% are shown to be effective at reducing shale permeability, thereby reducing the interaction between Atoka shale and a waterbased drilling fluid. This study shows for the first time that it is possible to formulate water-based muds using inexpensive nonmodified and commercially available silica nanoparticles and that these muds significantly reduce the invasion of water into the shale. The addition of silica nanoparticles to water-based muds may offer a powerful and economical solution when dealing with wellbore-stability problems in troublesome shale formations.

Characterization of Filter Cake Generated by Water-Based Drilling Fluids Using CT Scan

Abstract: Filter-cake characterization is very important in drilling and completion operations. The homogeneity of the filter cake affects the properties of the filtration process such as the volume of filtrate, the thickness of the filter cake, and the best method to remove it. Various models were used to determine the thickness and permeability of the filter cake. Most of these models assumed that the filter cake was homogeneous. The present study shows that the filter cake is not homogeneous, and consists of two layers of different properties. The objective of this study is to measure the filter-cake thickness and permeability of water-based drilling fluids by a new approach and compare the results with previous models. A highpressure/high-temperature (HP/HT) filter press was used to perform the filtration process under static conditions (225 F and 300 psi). A computed-tomography (CT) scan was used to measure the thickness and porosity of the filter cake. Scanning electron microscopy (SEM) was used to provide the morphology of the filter cake. The results obtained from the CT scan showed that the filter cake was heterogeneous and contained two layers with different properties under static and dynamic conditions. Under static conditions, the layer close to the rock surface had a 0.06-in. thickness, 10to 20-vol% porosity, and 0.087-ld permeability, while under dynamic conditions, this layer had a 0.04-in. thickness, 15-vol% porosity, and 0.068-ld permeability. The layer close to the drilling fluid had a 0.1-in. and 0.07-in. thickness under static and dynamic conditions, respectively, and it had zero porosity and permeability after 30 minutes under static and dynamic conditions. SEM results showed that the two layers contained large and small particles, but there was extremely poor sorting in the layer, that was close to the drilling fluid, which led to zero porosity in this layer. Previous models underestimated the thickness of the filter cake by almost 50%. A new method was developed to measure the thickness of the filter cake, and various models were screened to identify the best model that can predict our permeability measurements.

Drilling Automation: Presenting a Framework for Automated Operations

Abstract: Original SPE manuscript received for review 29 March 2011. Paper (SPE 158109) peer approved 29 December 2011. Summary This paper will present and discuss drilling automation on the basis of a “mode of automation” approach. Different modes of automation will be presented and explained. In particular, the paper will focus on how closed-loop control can enable higher modes of automation, which is essential to improve the operational and economic performance of drilling operations. Introducing a higher mode of automation may lead to optimal performance, but it also introduces new safety issues that need to be addressed in order to ensure safe conditions in the well. For each increased mode of automation, the work distribution between the automation system and the driller changes and a clear understanding of the human/ machine interaction at each mode of automation is needed.

A Technical and Economic Study of Completion Techniques in Five Emerging US Gas Shales: A Woodford Shale Example

Abstract: This paper (SPE 135396) was accepted for presentation at the SPE Annual Technical Conference, Florence Italy, 19–22 September 2010, and revised for publication. Original manuscript received 10 February 2011. Revised manuscript received 5 November 2011. Paper peer approved 10 November 2011. Summary With the increased demand for energy and the declining conventional hydrocarbons worldwide, energy companies are turning to unconventional resources such as shale gas. With more than 2,000 Tcf of gas in place indentified in just 5 shale gas plays in the United States, shale-gas formations are now the number one targets for exploration drilling. Furthermore, there are still many more major shale-gas plays and basins waiting to be explored, evaluated, and developed. Because of the extremely low permeability of most shale formations, it is essential to select the appropriate completion techniques for shale-gas reservoirs. There are very few papers in the petroleum literature that provide a logical method to select completion techniques for given shale-gas-reservoir conditions. There are papers discussing successful completion techniques that seem to work for a specific shale. We have used many of these SPE papers to help define “best practices” in completing shale-gas reservoirs. We then developed logic to determine the best practice in completing shale-gas reservoirs as a function of reservoir conditions. In this paper, we will specifically cover the logic we have developed for choosing completion techniques in shale-gas reservoirs. First, we performed a literature review on the five basins as well as on all shale-gas plays in the US to determine the best practices in shale-gas completion techniques in fluctuating price environments and identify key geologic parameters that affect overall well performance. From our literature review, we identified seven pertinent geologic parameters that influence shale-gas completion practices. Next, we identified different completion trends in the industry for different geologic settings. Subsequently, we generated an economic model and performed sensitivity analysis to determine optimal completions for each gas-shale basin. On the basis of these economic models, we developed decision flow charts to select completion techniques. Finally, we programmed the flow chart, and we call this program Shale Gas Advisor. This program can be used to determine optimum completion best practices not only for the five gas-shale basins discussed, but also for gas-shale plays that have similar geologic attributes. We validated the program with published case histories in the SPE literature.

Casing While Drilling (CwD): A New Approach To Drilling Fiqa Formation in he Sultanate of Oman--A Success Story

Abstract: Highly reactive Fiqa shale used to compel well engineers in the Sultanate of Oman to plan drilling phase of surface and intermediate sections primarily based on time exposure to aqueous drilling fluid water-based mud (WBM). The new approach of drilling the time-dependent Fiqa formation using casing-while-drilling (CwD) allows well engineers to plan prospective top/intermediate wellbore sections differently by enhancing the overall drilling performance. This reduces the risk of setting casing strings at unplanned depths, getting pipe stuck, or reaming continuously when drilling with conventional drillstring. The technical feasibility study, risk assessment, planning, execution, and the lessons learned during the process of drilling two top-section pilot projects are described in this document. The CwD team compares the drilling performance of several offset wells and suggests actions to improve the CwD technology in Oman. Two 171=2and 22-in. surface sections were drilled successfully with large-diameter casing strings and reached 754and 894-m measured depths, respectively. The implementation of the CwD concept reduced the overall drill/case phase time up to 40%, in comparison with the average using conventional drilling in those fields. Exposure time of Fiqa to aqueous environment was reduced by eliminating conditioning trips and nonproductive-time (NPT) associated with wellbore instability. Drilling both sections with non-retrievable 171=2 133=8-in. and 22 185=8-in. CwD systems did not require modification of well design or rig. The optimization of this technology will support its implementation as the conventional drilling approach in some fields in Oman.

A Dynamic Model of Percolating Gas in a Wellbore

Abstract: The two-phase dynamics of gas percolating up a vertical well filled with water is described by two ordinary-differential equations and algebraic relations. We model the gas as bubbles distributed with a distribution function along the well. The model is based on first principles and accommodates tracking of the front of the gas. An unscented Kalman filter (UKF) is used together with the model and wired-drillpipe (WDP) pressure measurements to estimate the liquid-holdup profile as the gas is circulated out of the well. The performance of the model and the method of estimation are compared with results from a state-of-the-art simulator.