  Generalising work of La Bret\`eche, Browning and Peyre and of the author, we
describe the geometry required by Manin's principle and Peyre's conjecture for
a family of conic bundle surfaces containing Ch\^atelet surfaces. These
surfaces $S_{a,F}$ are the conic bundle surfaces obtained as smooth minimal
proper model of $$ Y^2-aZ^2=F(X,1) $$ with $a \in \mathbf{Z}$ squarefree and $F
\in \mathbf{Z}[x_1,x_2]$ a binary form of \textit{even} degree $n$ without
repeated roots and whose irreducible factors over $\mathbf{Q}$ remain
irreducible over $\mathbf{Q}\left( \sqrt{a} \right)$.
