New Solutions for Subsalt-Well Lost Circulation and Optimized Primary Cementing

Abstract

fax 01-972-952-9435.References at the end of the paper. AbstractDrilling and cementing operations in certain subsalt wells in the Gulf of Mexico (GOM) and other areas have long challenged operators and contractors. These wells have thick, deep salt formations with shear zones just above and below the salt, resulting in high unexpected costs during drilling. Such formations are often referred to as rubblized or disturbed shale zones. One theory proposes that, during geologic periods, the movement of adjacent salt formations induces shearing stresses that cause deformation, brittle failure, and fracturing in the surrounding shales. Costly drilling problems in these zones are primarily caused by the narrow margins between pore and fracture pressures that result in severe lost circulation, hole instability, and high-pressure kicks. Some of these wells also exhibit uncontrolled gas flows and underground water flows. Many GOM deepwater blocks and shelf blocks have massive salt structures and potential hydrocarbon reservoirs, but the trouble costs and difficulties associated with drilling these wells have forced operators to plug and abandon some wells and completely avoid others.Conventional lost-circulation and hole-stabilization treatments have been minimally successful in many subsalt wells. However, new wellbore-stabilization and cementing programs designed for subsalt wells can help ensure well control and integrity during drilling and production operations. This paper provides information for helping to improve subsalt drilling operations and lower well-construction costs. In addition, the failures and successes of lost-circulation treatments performed during drilling operations in shear and salt zones will be explained. Primary cementing operations that help provide cost-effective zonal isolation and well integrity in these zones are presented, as well as best practices and proposals for cementslurry design and mud displacement. Laboratory studies and cost comparisons that help justify replacing traditional materials and procedures with these cementing programs are also presented.

Use of thermal analysis to determine the hydration products of oil well cement pastes containing NaCl and KCl

“…The AFm (Al 2 O 3 -Fe 2 O 3 -mono) phases refer a family of hydrated calcium aluminates with representative formula Ca 2 (Al,Fe)(OH) 6 ]ÁXÁxH 2 O, where X equals an exchangeable singly charged (e.g., chloride) or half of a doubly charged anion (e.g., sulfate, carbonate and aluminosilicate) [9,17]. When all calcium sulfate is consumed and the concentration of aluminate is high, the ettringite becomes unstable and it is gradually converted into the monosulfate (C 3 AÁCaSO 4 Á12H 2 O) [18].…”

“…This migration, if not considered, could result in a wellbore collapse [2][3][4][5]. Thus, saline pastes with sodium chloride (NaCl) and potassium chloride (KCl) have been commonly proposed for use in these environments to avoid unwanted changes in the properties of pastes [2][3][4][5][6][7].…”

“…20 % BWOW to saturation point of NaCl are used for pastes that are going to encounter salt zones and remain in contact with salt rock for the life cycle of the well [1]. It has been reported [2,6] that KCl can be used as alternative to NaCl in concentrations of 3-5 % BWOW. In most of cases, a 5 % KCl paste is considered to provide some protection against formation salt dissolution by the paste.…”

“…Although the salt influence in the fresh state and mechanical properties of the pastes have been studied by different authors [1,3,[5][6][7], few studies involving the hydration products of systems containing NaCl have been carried out [3,7]. Ludwig [3] studied the pore solution of the pastes with NaCl and concluded that the NaCl increased the solubility of calcium sulfate and accelerated the hydration reactions.…”

Visualization of salt-induced stress perturbations

“…Lack of consideration of the geomechanical interaction between salt bodies and surrounding formations has led to documented drilling failures adjacent to salt diapers [1] [21] [23], some cases resulting in individual well abandonment costs of tens of millions of dollars. To address this critical knowledge gap, a three-dimensional non-linear finite element geomechanical simulation effort was initiated to analyze the in situ stress state existing in, and adjacent to, salt bodies both before drilling, as well as under producing conditions.…”