Barite Sag Measurements

Abstract

Incidences with sag of solid weighting agents in drilling fluids can lead to potential drilling impediments including; loss of wellbore control, lost circulation, stuck pipe and high torque. The presence of sag has relatively often been the cause for gas kicks and oil-based drilling fluids are known to be more vulnerable for sag than water-based drilling fluids. Separation of weighting materials in a non-moving fluid column is referred to as static sag while sag in a flowing fluid is normally referred to as dynamic sag. An approach to obtain static and dynamic barite sag measurement protocols is presented to examine the effects of rheological and viscoelastic properties of typical field oil-based drilling fluids on barite sag performance. Static sag results are computed based on modified Stokes settling theory while dynamic sag results are compared for rotational and oscillatory ultra-low to low shear conditions. For static sag measurements, an optical scanning analyzer, which is based on the principle of multiple light scattering was used to characterize the stability and particles settling speed of the drilling fluid samples. A cylindrical glass cell containing 20 mL of drilling fluid sample was scanned at the entire height of the sample for 7 days at 1-hour interval to acquire transmission and backscattering data every 40 μm. Under the dynamic sag measurements, a rheometer with a measuring system applying a cup and grooved bob was used to conduct rheological and viscoelastic measurements such as flow curves, oscillatory amplitude sweep, oscillatory frequency sweep, rotational and oscillatory time tests on the drilling fluid samples. The drilling fluid properties were characterized under atmospheric conditions before and after dynamic aging. The aging temperature and pressure conditions in the roller oven were 120°C and 100 psi respectively for a period of 2-1/2 days. A high precision density meter was used to measure the density of the drilling fluid samples before and after each test. Dynamic sag index (DSI) results were compared between time-dependent rotational shear test with shear rates from 10.22 to 0.001 s−1 and time-dependent oscillatory shear test with angular frequencies from 10.22 to 0.001 rad/s at constant strain amplitudes of 0.05% within linear viscoelastic (LVE) range and 100%, over a period of 10,800 s to closely compare to sag-prone conditions during drilling operations. We observed that heat-activated chemicals in the hot-rolled fluid sample increased the viscosity and elasticity which contributed to lower barite sag and longer suspension of particles than before hot rolling. Moreover, rotational shear test increased barite sag in the fluid sample more than oscillatory shear test, particularly for shear rates exceeding 1.0 s−1. Within the LVE range, oscillatory shear test did not disturb the position of the particles enough to promote sag in the fluid samples. The time-dependent oscillatory shear test can provide new insight on the structural character of drilling fluids to predict barite sag tendencies during the fluid design phase.

Rheological and Viscoelastic Property Characterizations of Amino Acid-Based Hydraulic Fracturing Fluids

“…For evaluating the viscoelastic properties of the stabilized fracturing fluid, amplitude sweep tests were conducted on the system to (a) define the fluid’s LVER and (b) describe the dependence of the fluid’s loss moduli, G ′, and the storage moduli, G ″, over a given range of strain percentages (0.00025–100)% for a constant angular frequency (10 rad/s) at 25 °C. This provides necessary information needed to measure the viscoelasticity of the stabilized fracturing fluid . Upon the determination of the studied systems’ LVERs, oscillatory frequency sweep tests were conducted for those ranges to evaluate the stability of the systems’ elastic properties.…”

Enhancement of Static and Dynamic Sag Performance of Water-Based Mud Using a Synthetic Clay

“…These properties can be correlated with fluid stability to detect the solid sag phenomenon. − Ultrasonic and nuclear magnetic resonance methods were also utilized to analyze the sag tendency of the drilling mud by detecting the density stratification using the sound velocity and the influence of the magnetic field, respectively . Ofei et al also introduced another advancement in solid sag measurement using a cylindrical glass cell with the light scattering technique to characterize the homogeneity and settling speed of the solid particles in the drilling fluid.…”

Impact of Perlite on the Properties and Stability of Water-Based Mud in Elevated-Temperature Applications

“… 27 , 31 , 36 , 42 − 45 Monitoring of fluid density can be achieved by direct measurements, nuclear magnetic resonance (NMR) and ultrasonic technique, 25 and light scattering technique. 46 Another sag detection method is to monitor the rheological and viscoelastic behaviors of drilling fluids. 18 , 24 , 47 − 50 …”

“…These methods can be classified into three main categories: modify or replace the weighting agent with more stable material or a combination of weight materials, ,,,, add antisagging agents, ,− and implement sound techniques for early detection of the sag phenomenon and prepare rig crew for such situations . Lab measurements of the sag tendency are conducted to evaluate the effectiveness of these methods, such as sag tests that rely on the real monitoring of mud density using sag cells, flow loops, and viscometers. ,,,− Monitoring of fluid density can be achieved by direct measurements, nuclear magnetic resonance (NMR) and ultrasonic technique, and light scattering technique . Another sag detection method is to monitor the rheological and viscoelastic behaviors of drilling fluids. ,,− …”