Cleanup of Oil-Based Mud Filter Cake Using an In-Situ Acid Generator System by a Single-Stage Treatment

Abstract

Near-wellbore formation damage is expected during the drilling operations. Minimization, prevention, and removal of near-wellbore damage are essential to maximize well productivity. One of the major sources of skin damage is the residual filter cake developed by reservoir drill-in fluid (DIF). Therefore, an efficient filter cake cleanup method should be considered to enhance well productivity. Oil producers in sandstone reservoirs are being drilled with invert emulsion DIF during oil reservoir drilling. Standard completion of oil wells is with stand-alone screens. Although screens stabilize the wellbore and address sand control issues, it can also act as a trap for filter cake, resulting in high drawdown pressure. An in-situ acid-precursor technology, which generates organic acid, was proposed to be used. The prime advantage of this technology, especially in long horizontal wells, is the uniform distribution of acid during precursor to remove oil-based mud (OBM) filter cake by a single-stage. A special surfactant blend was incorporated in the cleanup fluid to alter the wettablity of the oily filter cake, and therefore, facilitate the reactivity of the produced acid with calcium carbonate particles. Detailed lab studies were conducted to evaluate the efficiency of the in-situ acid generator technology. The lab studies include various tests to evaluate filter cake removal efficiency, return permeability on real core samples, compatibility with formation fluids, and strength of dissolving calcium carbonate particles. Based on lab results, it was recommended to spot the single-stage filter cake cleanup fluid as a treatment for an oil well. This paper will discuss in detail the laboratory work that was conducted to evaluate the filter cake cleanup fluid performance. Introduction Minimization and removal of formation damage is an ultimate goal in drilling and completion designs to reach the target production rate. Field practices and numerous case studies have shown that near-wellbore damage is mainly caused by the drill-in fluid (DIF), which may result in major production restriction. The damage is caused by a form of external damage, such as mud cake. Invasion of mud solids and filtrate is a major source of the near wellbore damage (Almond et al., 1995; Leschi et al., 2006). The conventional near-wellbore damage removal or filter cake cleanup methods by chemical means are enzymes, chelating agents, reactive mineral acids, oxidizers, or a combination of these chemicals (Davis et al., 2004; Davidson, E. et al., 2006; Al-Otaibi et al., 2004). When it comes to removing an oil-based mud (OBM) filter cake, prior stages should be considered to these conventional treatments. The wettability of the oily filter cake particles must be altered from oil-wet to water-wet. This is usually done through multi-stages and consumption of large volumes of solvents, mutual solvents, and surfactants mixed in a carrying fluid. Eventually, for an operator, completing a well drilled with an OBM will be time-consuming and expensive using the mentioned conventional treatments.

Novel Cake Washer for Removing Oil-Based Calcium Carbonate Filter Cake in Horizontal Wells

“…In order to evaluate the NCW removal performance, the results were compared with three different studies that investigated removal solutions of filter cakes generated by oil-based mud with calcium carbonate as a weighting material, [46], [47] and [34]. Table 2 shows the filter cake removal efficiency, the retained permeability on sandstone cores, and the corrosion generated by the cleaning fluid for the aforementioned studies and for the proposed one.…”

“…In situ acid generation by acid precursors is one of the techniques in filter cake removal that delay the acids/filter cake particles reaction, resulting in a more even reaction rate over the treatment section. Binmoqbil et al [47] studied a combination of a formic acid precursor and surfactant for OBDFs' CaCO 3 filter cake cleanup. CaCO 3 solubility in the formic acid precursor was measured over time and temperature, which reflects the acid's strength and generation rate.…”

“…The procedure followed for the treatment design includes a solubility test for calcium carbonate particles in a novel cake washer (NCW) at different conditions, such as duration, temperature and acid concentration, a corrosion test of the actual casing joint at HPHT, and filter cake removal efficiency at 212 • F and 300 psi, and retained permeability on a ceramic disc and Berea sandstone core sample. NCW removal performance was compared with different studies that investigated removal solutions for filter cakes generated by OBDF with calcium carbonate as a weighted material [34,46,47]. The comparison against the presented study was conducted based on the filter cake removal efficiency, the retained permeability and the corrosion rate generated by the cleaning fluid, as possible.…”

Advancement in Acid-Precursor Chemistry for Removal of Drill-in Fluid Filter Cake

“…Esters of formic acid generally hydrolyze too fast (Binmoqbil et al 2009). While acetate and lactate hydrolyze slower, the generated acids do not possess sufficient dissolving power to effectively remove filter cake.…”

Optimization of a Solid-Acid Precursor for Self-Destructing Filter Cake

“…Chemical cleanup solutions for calcium-carbonate-based drillin filter cake include acids (Siddiqui and Nasr-El-Din 2005; Al-Yami and Nasr-El-Din 2009), chelating agents (Burton et al 2000), oxidizers (Almond 1982;O'Driscoll et al 1998), enzymes (Hanssen et al 1999), emulsions (Al-Riyamy 2000), solid-free brines (Al-Yami and Nasr-El-Din 2009), and in-situ-generated acids (Nasr-El-Din and Moajil 2007;Binmoqbil et al 2009;Alotaibi et al 2010).…”