Development of key additives for organoclay-free oil-based drilling mud and system performance evaluation

Traditional oil-based drilling muds(OBMs) have a relatively high solid content, which is detrimental to penetration rate increase and reservoir protection. Aimed at solving this problem, an organoclay-free OBM system was studied, the synthesis methods and functioning mechanism of key additives were introduced, and performance evaluation of the system was performed. The rheology modifier was prepared by reacting a dimer fatty acid with diethanolamine, the primary emulsifier was made by oxidation and addition reaction of fatty acids, the secondary emulsifier was made by amidation of a fatty acid, and finally the fluid loss additive of water-soluble acrylic resin was synthesized by introducing acrylic acid into styrene/butyl acrylate polymerization. The rheology modifier could enhance the attraction between droplets, particles in the emulsion via intermolecular hydrogen bonding and improve the shear stress by forming a three-dimensional network structure in the emulsion. Lab experimental results show that the organoclay-free OBM could tolerate temperatures up to 220 ?C and HTHP filtration is less than 5 m L. Compared with the traditional OBMs, the organoclay-free OBM has low plastic viscosity, high shear stress, high ratio of dynamic shear force to plastic viscosity and high permeability recovery, which are beneficial to penetration rate increase, hole cleaning and reservoir protection.

Calculation and application of partition coefficients of light hydrocarbons in oil-based mud system

To find out the relationship between the oil-based mud,the formation fluid and the extracted gas,we use a thermodynamic approach based on static headspace gas chromatography technique to calculate the partition coefficients of 47 kinds of light hydrocarbons compounds between nC5 and nC8 in two kinds of oil-based mud-air systems,and reconstruct the original formation fluid composition under thermodynamic equilibrium.The oil-based drilling mud has little effect on the formation fluid compositions in the range of nC5-nC8(less than 1%for low-toxicity oil-based mud and less than 10%for oil-based mud).For most light hydrocarbon compositions,the partition coefficients obtained by vapor phase calibration and the direct quantitative methods have errors of less than 10%,and the partition coefficients obtained by direct quantitative method are more accurate.The reconstructed compositions of the two kinds of crude oil have match degrees of 91%and 89%with their real compositions,proving the feasibility and accuracy of reconstructing the composition of original formation fluid by using partition coefficients of light hydrocarbon compositions between nC5 and nC8.

The utilization of spent palm cooking oil for formulating oil-based drilling muds with excellent H_(2)S scavenging capability

In this study,a spent palm cooking oil-based mud with an excellent H_(2)S scavenging capability induced by the inclusion of a small quantity of potassium permanganate is formulated and tested for the first time.The mud formulation,containing the spent palm oil as the continuous phase and water as the dispersed phase,respectively,was stabilized by Span 80 and rhamnolipid biosurfactant as primary and secondary emulsifiers,respectively,while hydrophobic zinc nanoparticles(NPs)were used as weighting agent.The results showed that H_(2)S scavenging capacity at the breakthrough time reached 182.4 g H_(2)S/barrel mud,which increased to 417.9 g H_(2)S/barrel mud at the saturation time,demonstrating the effective H_(2)S scavenging performance of the formulated mud.The spent palm oil-based mud(SPOBM)also showed a good flow behavior that could be well fitted using the Herschel-Bulkley and Casson models.The effect of temperature on the apparent viscosity of the SPOBM has been investigated,and the fitting of the viscosity-temperature data provided an estimate of the activation energy as 23.53 kJ/mol.The findings reported in this article reveal the feasibility of transforming the spent/waste cooking oils into a valuable commodity for formulating greener drilling fluids with acceptable rheology and excellent H_(2)S scavenging performance.

Oil Saturation Is Determined by Different Experimental Methods

Oil saturation was an important parameter of reservoir evaluation, which had important guiding significance for oilfield development. In this paper, the oil saturation of tight oil in G area was studied, and the original oil saturation of the study area was studied by using the comprehensive experimental method. The original oil saturation of tight oil in the study area was determined by J function method, rock electricity method and oil-based mud coring method. The results showed that through the comparison of three experimental methods, it could be concluded that the J function method leads to the low value of oil saturation in the study area. The oil-based mud coring method was more suitable for the determination of oil saturation in this area than the other two methods because it needs to meet too many conditions and the calculation results were also low. G area was located in Qili Village, Ordos Basin.

The behaviors of gas-liquid two-phase flow under gas kick during horizontal drilling with oil-based muds

Natural gas is easily soluble in oil-based muds(OBM),leading to complex flow behavior in wellbores,especially in horizontal wells.In this study,a new transient flow model considering wellbore-formation coupling and gas solubility on flow behavior is developed to simulate gas kicks during horizontal drilling with OBM.Furthermore,the effect of gas solubility on parameters such as bottom-hole pressure(BHP),gas void fraction and mixture velocity in the flow behavior is analyzed.Finally,several critical factors affecting flow behavior are investigated and compared to gas kicks in water-based muds(WBM)where the effect of solubility is neglected.The results show that the invading gas exists as dissolved gas in the OBM and as free gas in the WBM.Before the gas escapes from the OBM,the pit gain is zero and there is barely any change in the BHP,annulus return flow rate and mixture velocity,which means that detecting gas kicks through these warning signs can be challenging until they get very close to the surface and develop rapidly.However,in WBM drilling,these parameters change quickly with the increasing gas kick time.Additionally,for both cases,the longer the horizontal length and the greater reservoir permeability,the greater the decrease in BHP,and the shorter the time for gas to migrate from the bottom-hole to the wellhead.A larger flow rate contributes to a greater initial BHP and a lesser BHP reduction.This research is of value in characterizing gas kick behavior and identifying novel ways for early gas kick detection during horizontal drilling with OBM.