Selection and Qualification of Drill-ln Fluids for Horizontal Wells in Unconsolidated Sands

Abstract

Much of the development using horizontal well technology had been centered around drill-in fluids. These fluids tended to be excellent for completion purposes but poor drilling fluids, and although success was recorded throughout the world, many areas that required more robust fluids were not being drilled. Well conditions such as higher temperature >175 F), depleted sands, intermittent sand shale layers, low fracture gradient pore pressure spread, and high weights for wellbore stability were limiting the application of horizontal well technology. Not only were fluids not available to drill with, but also it was unclear what methods or techniques were needed for wellbore clean-up. Because of need for drill-in fluids, an effort was undertaken in concert with the service companies to develop fluids that met both drilling and completion requirements. The effort was systematic in that established criteria had to be met for both drilling and completion. These criteria included requirements on fluid rheology, thermal stability, lubricity, fluid-loss control, filtercake properties, and removal of filtercakes after drilling leading to low/no formation and screen damage. Laboratory tests to measure candidate drill-in fluids against these criteria were established. Both water and oil or synthetic invert fluids were developed. In this paper a quality procedure is shown for validating fluids on a screening basis followed by specific evaluation of methods to mix, maintain on the rig, and ultimately to complete. Our field experience has shown that this quality control procedure is crucial to the high success rate of Shell's horizontal wells in the Gulf of Mexico. Data are shown which lead to guidelines for drilling and completing wells with varying conditions. Introduction Shell Offshore Inc. has an economic requirement to obtain high optimum rates and high ultimate recoveries of oil and gas. This need has directed Shell's operating companies to develop technologies that are consistent with this economic driver. The implementation of horizontal well technology along with the use of Frac and Pack technology has resulted in higher rates and higher ultimate recoveries. Although Shell was not the first user of these technologies, Shell's operating companies have been especially aggressive in the application of horizontal well technology, especially in geopressured reservoirs in the Gulf of Mexico (GOM). The economic driver provided the basis for a focussed approach in the Shell E&P Technology (SEPTCo) laboratories, in concert with the major vendors to optimize the fluid technology associated with horizontal wells. A two-year effort has been ongoing to develop water- and oil-based muds which are effective over a range of weight from 7–18 ppg, of temperatures 40–250 F, and of differential pressures from zero to several thousand pounds per square inch. Because of the inherent problems with drilling shales, the need for higher rates of penetration, an opportunity to save a casing string, and greater use of polydiamond crystalline bits, a clear incentive exists for the development of nonaqueous drill-in fluids. P. 365

Development of New Drilling Fluids

“…The physical removal merits special attention. 5 During the initial stage of production, the filtercake caused a restriction of flow, requiring a high differential to overcome it. One important feature relates to how the whole filtercake or residual filtercake is dislodged from the formation.…”

“…The filtercakes can be detached easily or develop pinholes or tears, leaving a residual internal filtercake. The detachment of the filtercake is associated with the lift-off pressure concept introduced by Browns et al 5 and it is called in this research the minimum dislodging pressure (MDP). This pressure promotes breakdown of the filtercake.…”

“…The CEA 73 program debuted in 1995 to study formation damage caused by DIFs and cleanup technology for openhole horizontal completions. During the past years, Falla, 2 Serrano, 3 Gutierrez, 4 and Hale et al 5 have conducted their research on polymer-free (PF), sized salt (SS), and sized calcium carbonate (SCC) DIF systems. They carefully studied the formation damage and cleanup performance of these DIFs in horizontal well, unconsolidated sand completions.…”