Novel Environmentally Friendly Fluids to Remove Carbonate Minerals from Deep Sandstone Formations
- Mohamed Ahmednasreldin Mahmoud (Texas A&M University) | Hisham A. Nasr-El-Din (Texas A&M University) | Corine De Wolf (AkzoNobel)
- Document ID
- Society of Petroleum Engineers
- SPE European Formation Damage Conference, 7-10 June, Noordwijk, The Netherlands
- Publication Date
- Document Type
- Conference Paper
- 2011. Society of Petroleum Engineers
- 1.6.9 Coring, Fishing, 1.6 Drilling Operations, 1.8 Formation Damage, 4.1.2 Separation and Treating, 3.2.4 Acidising, 5.8.7 Carbonate Reservoir, 5.1.1 Exploration, Development, Structural Geology, 1.4.3 Fines Migration
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Carbonate minerals are present in sandstone formations. These minerals are either introduced to the formation during drilling/completion operations or naturally present in the rock. There is a need to remove these carbonates to enhance well performance. This especially true if there is a need to use HF-based fluids to prevent the precipitation of calcium and magnesium fluorides.
In this study, we introduced GLDA (L-glutamic acid-N,N-diaceticacid) a new environmentally friendly chelate to remove carbonate minerals from sandstone formations. We also compared its performance with available chelates like EDTA (ethylenediaminetetraaceticacid) and HEDTA (hydroxyethylenediaminetriaceticacid). Berea (5 wt% clays) and Bandera (11 wt% clays) sandstone cores were used in the coreflood experiments. The concentration of the chelates used was 0.6M at pH values of 11 and 4. The coreflood experiments were run at a flow rate of 5 cm3/min and 300oF.
Coreflood experiments showed that at high pH values (pH =11) GLDA, HEDTA, and EDTA were almost the same in increasing the permeability of both Berea and Bandera sandstone cores. GLDA, HEDTA, and EDTA were compatible with Bandera sandstone cores. The weight loss from the core was highest in case of HEDTA and lowest in case of GLDA at pH 11. At pH 4, 0.6M-GLDA performed better than 0.6M HEDTA in the coreflood experiments. The permeability ratio (final/initial) for Bandera sandstone cores was 2 in the case of GLDA and 1.2 in the case of HEDTA at pH of 4, and 300oF. At pH 11, HEDTA, EDTA, and GLDA almost were the same in enhancing the permeability of the Bandera sandstone cores. At pH value of 4, GLDA gave the best results in Berea and Bandera sandstone cores.
High temperature sandstone acidizing is challenging due to the very fast reaction rate and instability of clays at these temperatures (Ali et al. 2002). Gdanski and Scuchart (1998) have shown that essentially all clays are unstable in HCl above 300oF. The ideal stimulation fluid would remove the near-wellbore damage without depositing precipitates in the formation, and preventing well production declines due to solids movements.
Martin (2004) has showed that it was possible to stimulate sandstone formation without subsequent need for HF acid. The potential gain in the stimulation response was not be as great as that with HF-based systems. The benefits from using HCl alone in sandstone acidizing comes from the fact that quartz is not readily dissolved by HCl, therefore, HCl will dissolve the damaging materials not the matrix. By using HCl-based system many of the problems associated with HF can be avoided.
Flowing HCl in cores containing illite and chlorite caused the pressure drop to increase due to the clay reaction product migration, formation of reaction product and/or increase in the viscosity. Illite and chlorite are attacked by HCl to produce an amorphous silica gel residue i.e., the aluminum layer extracted. The alumina layer if attacked will weaken the clay structure and makes it more sensitive to fluid flow (Simon and Anderson 1990).
Thomas et al. (2001) showed that HCl degraded illite and chlorite in the tested cores from actual producing sandstone reservoirs. Degradation of illite and chlorite led to potential core damage. Treating the actual reservoir cores by mud acid caused fines migration during the post-flush.
Many problems may occur during sandstone acidizing with HCl/HF mud acid. Among these problems: decomposition of clays in HCl acids, precipitation of fluosilicates, the presence of carbonate can cause the precipitation of aluminum fluorides, silica-gel filming, colloidal silica-gel precipitation, and mixing between various stages of the treatment (Gdanski and Shuchart 1998).
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