A new in-situ generated HCl acid was developed to overcome the fast reaction rate and high corrosion rates of 15 wt% regular HCl acidizing system. The objectives of this work are to: (1) examine the reaction rate of the new in-situ generated HCl with calcite at 100, 150, and 200℉, and (2) compare the reaction rate of 15 wt% regular HCl with the new in-situ generated HCl. The rate of the reaction of 15 wt% HCl and the new in-situ generated HCl was measured using the rotating disk apparatus (RDA). Calcite disks were used with the specifications of 1.5 in. the diameter and 0.65 in. thickness. The effects of disk-rotational speed (200-1,200 rpm) and temperature (100-200℉) were investigated. Calcium concentrations were measured in the samples collected from the RDA, which were used to calculate the rate of dissolution. The disk surface after the tests was analyzed using Scanning-Electron-Microscope–Energy-Dispersive Spectroscopy (SEM-EDS). Experimental results showed that the rate of dissolution at 100 and 150°F was controlled mainly by the rate of mass transfer of the acid to the surface. By increasing the temperature to 200℉, the overall rate of reaction for the in-situ generated HCl was mass transfer limited up to 800 rpm and surface limited above 800 rpm. Based on the dissolution rate results, the diffusion coefficient, the activation energy, and the reaction rate constant at 100, 150, and 200°F were determined for the new developed in-situ generated HCl and were compared to 15 wt% regular HCl. This study will assist in developing a more cost-effective and efficient design of acid treatments through a slower reaction rate of the in-situ generated HCl. This new in-situ generated acid system reacts slower and more efficient compared to regular HCl in carbonate and sandstone reservoirs.

Sand and fines production is one of the oldest problems in petroleum industry and one of the toughest to solve. Today, many active and passive technologies and methods exist; in some cases some sand and fines production is manageable, while for others it cannot be tolerated at all. Also, many wells do not produce sand or fines from the onset and may not require an active sand control solution until later in their live. Chemical sand control solutions have been around for many years have always been attractive due to their ability to be installed without any restrictions to the well bore geometry. However, due to the difficulties with placement and in many cases their association with some degree of reduction in permeability there has been some reservation to use chemical methods as a standard. This paper presents a unique chemistry that not only increases the maximum sand/fines free rate without a significant reduction in permeability, but also discusses the advanced placement techniques essential for a successful application. This paper includes study of two hundred and fifty wells which has been treated by using zeta potential altering chemistry and shows analysis of both failed and successful applications and the lessons learned.

It is challenging to remove filter cake uniformly and thoroughly from the production interval in horizontal and multi-lateral wells with heterogeneous formation characteristics. The inability to obtain complete filter cake removal is a common occurrence with the currently available reactive fluid systems. Another instance where conventional reactive systems are not adequate is when it's desirable to spot the treatment fluid prior to running final completion. In some instances, this kind of operation can take several days.Conventional practice to remove filter cake formed by water-based drill-in fluid usually includes strong mineral acids, buffered organic acids, oxidizers, enzymes, and chelating agents. These systems all have limitations that can result in nonuniform clean-up of the filter cake. Certain esters of organic acid have been investigated and used for filter cake removal to achieve better zonal coverage by delaying acid release. However, esters of formic acid generally hydrolyze too quickly, while acetic and lactic acid precursors hydrolyze more slowly but are not strong enough to effectively remove filter cake. This paper presents a new delayed-release acid system that can generate an organic acid in situ. The system hydrolyzes more slowly than formates and lactates in the medium-to-high temperature ranges, and the generated organic acid is stronger than formic, lactic and acetic acid. Laboratory studies with a static HT/HP filter press demonstrated this new system can clean up filter cake effectively. Laboratory evaluation also demonstrated that polymer-specific enzymes can be added to the system to enhance clean-up efficiency because of its long delay time. Compared to conventional chemical methods of filter cake removal, this new delayed-release acid system provides a more efficient alternative, especially when the completion activity requires a long system delay time before the clean-up acid will be released across the entire production interval.

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